UngeheuerLich
Legend
Quite a few classes could have some features of their most iconic subclasses baked in. Fighter could have battlemaster maneuvers or at least all the champion stuff by default.I have an incredibly difficult time articulating why the D&D monk disappoints me so much. I could think of a few easy quality of life changes that I think would really benefit it, but nothing that really solves my core issue of it being so unenjoyable for me despite being the closest thing to style of character I most enjoy playing (supernatural martial artist). Giving the base monk the Way of the Open Hand's Open Hand Technique would go a long way towards making them feel like martial controllers, which I personally think is a good niche for them to occupy separate from the other martial classes. Improve the Unarmored Movement ability so that it imposes Disadvantage on enemy Attacks of Opportunity, and you have a much stronger incentive and ability to stay mobile.
Honestly, 5E as a whole would have worked a lot better if they had taken a page out of Fantasy Craft's book and given each class a "Core Ability" that you only get when you start as that class. Then they'd be able to stop worrying about giving classes fun abilities earlier on that get collected via dipping.
The ranger could have some hunter features baked in, or the beastmaster pets.
The rogue could have the thief features always active...
WotC probably was a bit conservative in giving archetypal features to the base class, because they may not be what you want.
I like what they did with the warlock in principle. A subclass and on top a few choices to pick from afterwards (pact of the X and invocations).