I agree with your point, but I must correct you on DOS: it had device drivers too. :) That's how we used to access mouse input, CD drives, network, extended memory, etc. Yes, it sucked on the graphics and sound; every app basically had to reimplement its own graphics and audio layer from scratch, but the rest was quite abstracted away.

There were generic VESA SVGA drivers towards the end of the MS-DOS era.

Sound blaster(16) also came close to being standard enough that games could just support that.

Extrapolating I think MS-DOS was on a nice trajectory to having complete enough (and reasonably simple and non-bloated!) APIs for everything important, when it was killed off. Late MS-DOS 32-bit games were usually trivial to install and run.