At level 3, warlocks gain the Pact Boon feature, and one of the options is Pact of the Blade. One of the benefits of the warlock’s Pact of the Blade is the ability to conjure any melee weapon the warlock likes, and for the warlock to be proficient in that weapon:
You can use your action to create a pact weapon in your empty hand. You can choose the form that this melee weapon takes each time you create it. You are proficient with it while you wield it. This weapon counts as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage.
This received a lot of attention when discussing monster-only weapons like the ice devil’s spear, but developer commentary nixed that combo, barring perhaps if you get proficiency elsewhere and become legitimately Large yourself.
Without such weapons, though, this feature looks rather difficult to leverage: the game rewards specializing, but if, for example, you build around a high Dexterity, non-finesse weapons are basically useless to you. If you instead multiclass with fighter and take the great weapon fighting style and the Great Weapon Master feat, then non-great weapons aren’t worth your time. The Hexblade patron goes a long way towards solving the biggest problem here, multiple-ability dependency, but does nothing about the difficulty leveraging feats, and in any event the Hexblade may not be available in every campaign.
So this is my question: what is the best approach to getting the most from the ability to use any weapon I want? Ideally, a build that switches between weapons on the fly for different situations. Importantly, I want a character that has a reason for using so many weapons—if having just one weapon, or just relying on eldritch blast, is strictly-superior to a given approach, that isn’t an answer to the question—it’s a claim that the build simply is not supported by the system at all. Which may well be true, but be prepared to back that claim up.
Crucially, how having multiple weapons is advantageous is up to you: if eldritch blast cannot be beat for damage, for example, then a build that uses weapons for utility somehow would be great, where a build that goes for damage and just ends up worse than eldritch blast would not. But since I am not an expert in 5e, and don’t know the answer to my own question, I am explicitly looking for answerer’s expertise and judgment in how to best leverage this feature. I have offered my expertise and judgment on similar questions for D&D 3.5e many, many times, so I know this is a thing people are capable of doing.
Feats are allowed, and so is a limited amount of judicious multiclassing—but answers with less multiclassing are better. Ideally an answer considers a build’s progression from 1st to 20th, but an answer that focuses on a somewhat narrower range—explaining why it doesn’t work before that range or why it fails to grow beyond that range—is acceptable. For reference, but not as a restriction, my particular character is starting at 4th level.
Please be specific about what sources you use—nothing is completely off the table, including Unearthed Arcana, but answers that use fewer sources are better. In particular, anything that’s not in Player’s Handbook should note why it’s important and what, if any, substitutes might be available from Player’s Handbook-only play.
The reason I ask for those notes is that I am joining a game with mostly new players, and while the DM seems amenable to me making light usage of supplemental materials, I very much don’t want to push it or overburden him, or outshine my fellow players. Nonetheless, I worry that without the Hexblade, there just isn’t really a good way to do this. So I want to know what the options are, so I can make my own judgment about how much is worth asking for.