Warlock gets singled out because, in 5e, their magic works differently from just about every other magic-user. I don't think this is a problem with the Warlock, I think it's the result of every other magic-user using more-or-less the same system for their magic.
I have zero familiarity with 5e, but based on previous editions I definitely agree. The problem isn't that the warlock is weird, it's that everything else is so samey. Almost all spellcasters work the same, with a few exceptions that rarely get any traction. Psionics is probably the biggest secondary method, and it's always struggled for attention and balance. In general I'm in favor of more oddities, not less.
I’m at the opposite end. While I’m not a fan of Old D&D or D&D’s spell casting system (mostly BC of the Vancian system and arbitrary spell levels with inconsistent power), one of the things that OD&D handles better than WotC era D&D is character classes. 3e+ D&D is a bloated mess of artificially distinct character classes that are essentially variations of warriors, casters and specialists/rogues (the only three classes that should exist) with an overinflated mess of fiddly features that are hard to recall and add to bookkeeping. I prefer streamlined classes that follow an easy to remember minimalistic and standardized pattern of core features that I can use on the fly to improvise NPCs or automatically know what abilities PCs have without having to consult the manual to determine which of hundreds of fiddly barely useful features that class gets each level. And to leave the entirety of the complexity and distinctiveness to Skills, Feats and perhaps backgrounds and/or 2e style “kits”, where they belong.
All that having one hundred and fifty thousand “different” classes that are really just casters, warriors or rogues does is complicate the game and add a bunch of inconsistent, hard to track and often arbitrarily level-gated features that add to bookkeeping and lead to an out of control spiral of ever expanding artificially distinct classes every time someone has a different take on what the thing they call “warlock”, “paladin” or “wizard” should be like. And on the topic of casters in particular, you don’t have an entirely different combat system for every single warrior class. Combat is just combat. An individual warrior may have one or two different tricks up their sleeve (preferably acquired through feats), but they all use basically the same consistent combat rules.
Casters should be the same. The game is already complicated enough with an over-bloated list of hundreds of arbitrarily level-gated spells that are really just variations of “causes fire damage”, “reads minds” or “heals damage”, etc., without adding to it by also giving every caster class an artificially distinct system to ultimately just cause fire damage, read minds or heal damage. Differences should be RPed or based on skills, feats or background-type stuff that simply adds to a baseline core class rather than reinventing the wheel every time someone has a new take that’s really just a warrior...but sneaky, a wizard...but has pets, or a rogue...but has a few spells.