No
The Help action clearly states
You can lend your aid to another creature in the completion of a task.
Even if you read it separated from the second paragraph
Alternatively, you can aid a friendly creature in attacking a creature within 5 feet of you.
Here, Crawford clearly states that "friendly creature" referes to someone else, not yourself, and even explains that, as in Inspiring Leader, if you could target yourself, it would state it explicitly.
Is a creature its own ally? Also probably no.
I would like to add another point: even if in 5E it might not be explicitly written, it is almost certainly intended that "an ally" is another creature (Note: As soon as I wrote that, I sanity-checked myself and got some doubt. Then I opened this question, so refer to it in case I'm wrong here). Check, for monsters from the Monster Manual, the feature
Pack Tactics. The wolf has advantage on attack rolls against a
creature if at least one of the wolf's allies is within 5 feet of the
creature and the ally isn't incapacitated.
If the Wolf counted itself as an ally, this feature would be "the Wolf always has advantage on attack rolls", since it can only attack from melee (within 5ft.) and can only attack if he is not incapacitated. If this was intended, it would probably just say so.
The specification:
Starting at 3rd level, you can use a bonus action to make a Perception check to spot a hidden creature or object or to make an Investigation check to uncover or decipher clues.
Suggests that a bonus action specifically will be useful - meaning that the Investigation check will be useful in a combat or other time-crunch scenario.
Uses for Investigation checks
Taking some examples from the DMG on how an Intelligence (Investigation) check might be used in combat:
Perhaps your party is being chased by a powerful adversary, and you need to escape a dead-end room. DMG 104:
Opening a Secret Door. Once a secret door is
detected, a successful Intelligence (Investigation) check
might be required to determine how to open it if the
opening mechanism isn't obvious.
Perhaps your party is engaging an enemy in a battlefield that the enemy had the chance to prepare. Detecting and disabling the traps for yourself or your allies is key. DMG 121:
If the adventurers detect a trap before
triggering it, they might be able to disarm it, either
permanently or long enough to move past it. You might
call for an Intelligence (Investigation) check for a
character to deduce what needs to be done, followed
by a Dexterity check using thieves' tools to perform the
necessary sabotage.
There's plenty more ways, depending on how combat goes. You might need to quickly figure out how to use the MacGuffin to annihilate the baddy, or spot a clue as to their social ties that you can use for leverage.
Balance
The Swashbuckling Rogue Rakish Audacity feature:
[...]
You also gain an additional way to use your Sneak Attack; you don't need advantage on the attack roll to use your Sneak Attack against a creature if you are within 5 feet of it, no other creatures are within 5 feet of you, and you don't have disadvantage on the attack roll. All the other rules for Sneak Attack still apply to you.
Only really works for one-on-one fighting, you can have neither allies on your side, nor additional enemies. While it is certainly powerful, it's not quite an always-free Sneak Attack.
And the Panache feature:
[...] If you succeed on the check and the creature is hostile to you, it has disadvantage on attack rolls against targets other than you and can't make opportunity attacks against targets other than you. This effect lasts for 1 minute, until one of your companions attacks the target or affects it with a spell, or until you and the target are more than 60 feet apart. [...]
This feature occupies a different niche than the Inquisitive Insightful Fighting feature. Panache is more of a support feature, making the enemy less likely to hit your allies, while Insightful Fighting helps you deal damage directly. The value this brings to you depends on your team composition and tactics.
However, you're right in that the Inquisitive subclass is altogether weaker directly as compared to the Swashbuckling subclass. Initiative and Attacks of Opportunity are all things that take part in every combat, whereas having the combat depend on your character quickly identifying some tipping point is a lot more circumstantial. If you want your Inquisitive Rogue to use their class features in combat more, and in a meaningful way, you should talk to your DM about it. The examples above show that there are ways to make Investigation useful in combat, it then falls on your DM to give you these opportunities.
Best Answer
Insightful fighting is a good option to have
Yes, attacking with advantage, as well as sneak attack, when hidden is great, but there are at least two reasons that Insightful Fighting could sometimes situationally be the better choice for your bonus action.
Just because your Rogue has Cunning Action and can hide as a bonus action doesn't mean that hiding is an always available option. The location of your combat is vital. You're unlikely to have many fights on an endless unbroken plain but that doesn't mean that there's always going to be a good place to hide within 30 feet. Hiding may not always be possible - though it'll be easier if you're a lightfoot halfling so can hide behind other players.
If you're using your bonus action to hide you only benefit from it on a single attack. To get the same benefit next turn you'll have you use your bonus action to hide again and so on, for as long as the combat lasts - that rules out any other possible uses you have for your bonus action.
Insightful fighting on the other hand could last for an entire minute. Once you pass the check, and gain the benefits of Insightful Fighting, they're active for up to 10 combat rounds (ending prematurely if the creature dies or you use the feature on a different creature). Not many combats last that long, but against one or two big enemies, as opposed to lots of minions, that's up to nine rounds where you can do something else with your bonus action. Sure you don't have advantage on each attack - but now (among other possibilities) two weapon fighting is an option. If you miss once you get a second chance to hit with your sneak attack (and two chances to crit) - and if you're lucky you could hit twice.
A final reflection:
Insightful Fighting is on the whole going to be more useful for melee rogues, who will find hiding more difficult. To attempt to hide they'd often have to take an attack of opportunity, as they won't be able to use their bonus action to both hide and disengage on the same turn.
Conversely, it's going to be less useful for ranged rogues, who won't benefit from two weapon fighting and won't have any need to disengage - but it can still be a useful choice for either of these players. Both these rolls have a chance to fail, so a ranged rogue might choose to hedge their bets by using Insightful Fighting to guarantee sneak attack for up to ten rounds and then still attempting to hide with their bonus action on subsequent turns to gain advantage as well.