Just out of curiosity, what modern game won't function with a generic HID game controller?
But it's all a bit theoretical, since most modern gamepads have Xinput support, and the generic HID devices are mostly flightsticks or SNES-style gamepads that wouldn't have enough buttons and axis for modern games in the first place. Another issue is that most games don't offer input remapping for gamepads.
But with SteamInput and homebrew tools like x360ce there are many ways to make generic USB devices compatible Xinput, so it's not like you can't use them. It's just not something that works out of the box.