What can you build without Feats and MCing?

[col_impact]

Without MCing and Feats, the playstyles available to the players are determined by the class they choose, and rarely (in the case of Hexblades and some Cleric subclasses) the subclass. The only outliers are Warlocks having their Invocations and Pacts. Beyond that, there's no adjusting your build to a new playstyle, what you choose is what you're stuck with. Good luck.

Wizards offer a lot of flexibility. Bards do as well with Magical Secrets.

[Mimersbrønd]

Friends don't let friends play dwarves.

But best friends play only dwarves

dwarf best race

[Willie the Duck]

As usual, it all depends on what you are looking for the game rules to do. It also depends on what you are looking for 'permanent' effects to do. You can create variability by switching between using a greatsword and a pair of axes, or memorizing fewer crowd control and more mobility spells, or the like. As mentioned, much of AD&D (also much of basic/classic/non-advanced TSR-era D&D) didn't have a lot of character 'build' to the system, but individual characters were still differentiated (more than by RP decisions). Oftentimes it was by what magic items you acquired. Other times by what retainers and hirelings you brought with on adventures (in this case considering those as mechanical effects rather than RP effects, although they are both). Joe the fighter with the trident of fish command and a flying carpet who has a retinue of defeated former enemy 'humanoids' as his hirelings was decidedly different from Jim the fighter with the sunblade and ring of spell turning who hired a bunch of family members as his henchmen.

Barbs also kinda use 3 stats, and they still get jipped pretty hard by no feats.

Barbarians and Samuria&Champion fighters (sadly the kind that AD&D-era gamers might most want to play) certainly do miss their -5/+10 feats and the like. Even Eldritch Knight fighters can do pretty well without feats.