Was that a question? In my opinion it made PC gaming much better, in the long run (not overnight).

DirectDraw and Direct3D opened up the hardware market to more competition. Before that you either had a 3Dfx Voodoo (2) card or such, but its monopoly got broken with Win9x and other 3D graphics HW vendors started making much more advanced graphics cards. NVidia and ATI/AMD cleaned the table.

DirectInput allowed more precise flightsticks, and all new kinds of gaming controllers with far more buttons.

Same for sound cards, suddenly you didn't need any "Soundblaster compatible", even the basic onboard audio chip on your motherboard was enough. Certainly most DOS games supported various sound cards, but since the support wasn't on OS level, you couldn't e.g. use a new sound card with those old DOS games, unless it was hardware compatible with one of the supported older sound cards.

All in all, Win9x allowed PC gamers to choose from a wider range of components and peripherals, which both brought new kinds of components to the market, and made PC gaming more affordable.

All of the games that I can remember seem to have been available for DOS as well.

If I remember correctly, I always liked playing in DOS better because the music/sound fx sounded better - I can't remember the technical reason why though.