To make your question short, and to see if I understood it correctly, we're talking about a player who made his character a certain one and roleplays it entirely different. You added that you think that it comes from inexperience, and that he created this character after you said "no" to some "freak-character"-ideas. You want to help him roleplay the character he created.
As I see it, this problem is made from two smaller ones. The first is that he doesn't see his character as interesting because the character "is normal and normal is boring". The second is that you wanna help him understand why the way he plays the character does not fit the story-world of your game.
Helping him understand that "normal is not boring
This is the more important problem, as it stands in the basis of the entire problem. If he'll see that normal characters can be interesting his "anti-persona" will perish and he'll roleplay a normal character and not a freak one. The main trick here is to show him that normal characters are not entirely normal, i.e. "no person is like the others". In order for that to work, we need to give the character depth.
The easiest way to give depth to a character is through internal conflicts. Having goals and all is nice, but without something that blocks oneself from achieving them it is far less interesting. First thing to do is to go over his character's background and see if he implemented there an internal conflict for his character. If so, show it to him and talk with him about it. If no, sit with him and help him to come with one. The internal conflict doesn't have to be extravagant, but it needs to be there. An example one might be that he loves Vincent's sister but secretly hates Vincent himself, or another like Loves the sister but thinks that he's not good enough for there. I'll take the second one as an example for this section.
The conflict gives us a few things, a few added benefits. It gives the character 2 conflicting goals: "Get the sister and prove that I'm worthy". Now, with those two we also get a kind of an achieving-plan: "If I'll show her that I'm worthy, by getting something amazing done, she'll want me and I'll be able to get her". More than that, the character gets the knowledge that each advancement in order to achieve one goal will drive the other one to the far end.
But the first conflict is even more interesting. The character here has the knowledge that he needs the brother in order to save his lover, but he just can't stand being near the brother. He'll drive the mission onward for two reasons but he'll have doubts about his lover- if he'll marry her he'll be stuck with this brother of hers.
To make long story short, simple conflicts can show the player that even normal characters are interesting and unique. When combined with goals they force the character to take certain steps along the roads, to commit certain actions along the way, that he won't want to do but will make him doubt himself and question himself and see that his problem are far more interesting than those of every freak that he'll encounter.
Another nice way to help him see the importance of conflict is through showing him and analyzing with him certain protagonists that are normal people, from the stories and movies and series (of any form)that he likes. He'll see quite quickly that the conflicts make them interesting.
But he may say that it is not enough. For that there are a few more literary tools that might help him see why normal people are interesting. The first one is having flaws (internal or external) and the second one is using "The Ghost".
Flawed characters are characters that just like normal people aren't perfect. Those flaws can be internal (self-doubts, for example, or a mild paranoia) or they can be external (they're look frightens ordinary people, for once, or a missing hand for the other). The idea is that the character has to deal with the flaw, and one day to find the strength to overcome it. The fight for the overcoming act makes the character far more interesting. A nice example of that can be seen in The Rain Man, where he learns at the end that he can count on strangers/"dumb" persons like he's brother. Another nice example can be seen in the story of The Ugly Duckling who although looking terrible learned to acknowledge himself and to accept the way he looks, to accept his difference.
"The Ghost" is an event from the past that just like a ghost haunts the character to this day. Again, trying to cope with it is what builds a deep character. One example for this can be seen in the movie Inception, where we literally have a ghost- Cob's wife. Another example for this can be seen in the movie Casablanca, where he has to deal with his broken relationship with Ilsa. This Ghost is far more interesting as the originator of the Ghost actually comes back to his life. In Frozen we see another kind of a Ghost- the act that one feels guilty about. Elsa actually killed her sister.
All of these techniques are there for one reason- to make regular people interesting, to give depth to the characters, to make them human beings with goals and drives and psychology.
Helping him see that his character doesn't fit the world
After he understands that he doesn't have to be a freak in order to be interesting, he will be far more understandable about playing a character that fits the world. Then, try to explain to him as calmly as you can what it is in the way he played his character that doesn’t fit the world.
Explain to him that the characters are in a world where being a freak is bad, where achieving one's goals is the ideal. Each and every one for himself, as the saying goes. Give him examples from the way he played his character and analyze with him, in a one-on-one conversation where his way of acting came from. Use the background he created to illustrate to him where your problem comes from.
Then ask him what problems he has with his character, and together try to find a solution. Maybe let him be just a little bit freakish. Maybe he needs to just create a different character. This is basically between you and him. After that show the updated character to the group and get their approval.
When combining those two, you'll get a player who his far more willing to both play the character while also seeing the problems with the way he played his character before.
Combining the two solutions
When combining the two solutions you get a better player, who understands for the future also how to create regular characters that are not freaks yet far more interesting than those freaks will ever be able to be. Furthermore, you get a player who is willing to play his character as written while still making the character fit into the world. Hope any of these helped you.
First, lets kill the metagaming ad hominem: "Metagaming is any strategy, action or method used in a game which transcends a prescribed ruleset, uses external factors to affect the game, or goes beyond the supposed limits or environment set by the game. Another definition refers to the game universe outside of the game itself."
Optimising a combat-oriented character to be good at combat within the rules is not and never can be metagaming. You can't even mount a game universe argument that it is: a person who has devoted his life to being a wilderness warrior (aka a Ranger) is going to learn to be good at fighting or die!
Your hit point edge is insignificant; an 11 hp advantage is, on average, 2 hits or 1-2 rounds more staying power in a combat (less if fighting multiple foes). When you consider that the Paladin has an ability to heal 15 hp with their Lay on Hands ability at the cost of an action, they effectively have more hp than you do. You do have a definite advantage if you are being hit by things like fireballs; on failed saves you are the only one left standing.
This is an edge but a small one.
I will assume everyone has the same stat modifier on damage rolls.
If you are using your bow and choose to use a spell slot for Hunters Mark, you can do 3 + d8 (bow) + d6 (Hunters Mark) (avg 11) on the first hit and the same plus d8 (Colossus Slayer) (avg 15.5) on subsequent attacks. This is great if you are fighting a monster with lots of hit points; it is not so good against a dozen goblins since the first hit will drop them and your Colossus Slayer never kicks in.
Meanwhile the Paladin with a longsword and the dueling fighting style is doing 3 + 2 + d8 (longsword) + 2d8 (Divine Smite) (avg 18.5) (I haven't considered some of the really cool spells they have).
The Rogue is doing 3 + d8 (longbow) + 2d6 (sneak attack - a good rogue should almost always get this) (avg 14.5).
The Sorcerer has a plethora of options (Magic Missile, Burning Hands, and Cloud of Daggers spring to mind) or they can just fall back on a damaging cantrip for d10 (avg 5.5). If they are a gambler, Hold Person can end a combat with a single humanoid on one failed saving throw.
If the Bard wants to be handing out massive damage in combat then they chose the wrong class; that is not where their talents lie, they are an enabler - they enable others to do more damage.
The Ranger is not the best at handing out damage.
Overall, you are playing your character to his strengths; are the other players playing to theirs?
Pacing and Encounter structure
You say "I was typically able to go first in any combat due to high DEX, and dealt such insane damage that the guys going last did nothing".
I read "The encounters are underpowered".
Don't misunderstand me: it is the nature of RPG that the PCs will win (almost) every fight because they can only lose once. Most combats will be and should be cakewalks, they are there because combat is fun and they consume resources. That said, they shouldn't be so insignificant that they are over before the first round ends. A quick combat like this is great if the players have planned and executed a great ambush, its not great if it is just way underpowered.
If you have enough spells to use a spell in every combat then you are not having enough encounters between long rests. Burning through spell slots for a non-core spellcaster should be a tough decision: "Do I use it now or will I need it latter?" If you are not thinking this, at least briefly, all the time then your DM is being easy on you. Fights early in the day will usually be easy but this is due to everyone having lots of resources, as you burn through spell slots and hp the same encounter becomes much harder.
Also, the structure of encounters matters. 5 PCs on one monster is an easy fight (unless the monster's CR is extremely high for the party); the monster can only target 1 PC while copping damage from all 5. 5 PCs on 5 monsters is much harder; the tough PCs have to control the battlefield or the squishy PCs will get squished. 5 PCs on 15 monsters, even very weak monsters, is really hard; everyone is copping damage and the fight will last 4-5 rounds minimum.
It sounds like your fellow roleplayer just wants you to be verbally clear about what exactly you're doing mechanically without just pointing to a thing on your character sheet. It doesn't sound like their problem is that you're roleplaying at all—I'd be pretty surprised if they disliked flavourful descriptions of how people do things.
It's pretty easy to verbally express what you're doing mechanically and what you're doing flavourfully side by side. Doing one doesn't preclude doing the other. You could say something like this:
Then your DM knows what's going on both in terms of mechanics and roleplay, and your fellow player does too, and nobody has to squint at your character sheet or have it held up to them whenever you do something for them to know what's going on.
This isn't “against roleplaying.” It's just good communication. I roleplay regularly in my own games—I just say what I'm doing mechanically at the same time. Let's not misrepresent what will be happening: you're not going to be repeating “bard” again and again, you'll just be stating “bardic music” when that's what you're using. If the name bothers you then you could rename it to something you find more satisfying, like Fascinating Voice.
Maybe your specific brand of roleplaying involves avoiding any verbal mechanical description, but you should understand that's going to make things difficult and frustrating for some people.
Think of it this way: people are pretty bad at focusing on multiple things at once. Your fellow players can either focus on listening to you and watching you, or they can focus on looking at your character sheet and trying to read what you're pointing at, but they can't do both very well. Ever been to a talk where the presenter had a dozen bullet points on their slide, and if you tried to read them you'd realise you weren't absorbing what the presenter was saying? It's going to be like that.
So really, verbally stating what you're mechanically doing allows your players to focus entirely on watching and listening to you, meaning they can follow everything you're doing easily. That supports roleplaying and makes it easier for you and everyone else. Not doing this is more likely “against roleplaying” since it makes it harder for people to understand you.
You could talk with them and find out what will help accommodate them, but really I suggest you just accommodate your fellow player and take this as a lesson on communication.