PS4 controller support on Windows used to be a huge hassle, because you had to install DS4Windows to make it work. Nowadays, Windows automatically downloads the proprietary drivers to make it work, but I'm not sure if that covers the PS4 controller-specific features such as the touchpad, gyroscope, lightbar or if it enables XInput support. I think the PS4 controller situation supports what OP above is claiming.
Note: the Windows support is a WIP and the devs don't have the new Steam Controller
It would be better if they released drivers instead.
If you had rosetta it would be able to self-update to the new universal binary, without it you have to do this one update manually.
$ file steam_osx
steam_osx: Mach-O universal binary with 2 architectures: [x86_64:Mach-O 64-bit executable x86_64] [arm64]
steam_osx (for architecture x86_64): Mach-O 64-bit executable x86_64
steam_osx (for architecture arm64): Mach-O 64-bit executable arm64
% file /Volumes/Steam/Steam.app/Contents/MacOS/steam_osx
/Volumes/Steam/Steam.app/Contents/MacOS/steam_osx: Mach-O universal binary with 1 architecture: [x86_64:Mach-O 64-bit executable x86_64]
/Volumes/Steam/Steam.app/Contents/MacOS/steam_osx (for architecture x86_64): Mach-O 64-bit executable x86_64% file steam_osx
steam_osx: Mach-O universal binary with 1 architecture: [x86_64:Mach-O 64-bit executable x86_64]
steam_osx (for architecture x86_64): Mach-O 64-bit executable x86_64
A custom driver could always be made by the community. It feels a little absurd to expect Valve to write and support four different gamepad drivers, when they only need one.
That is what the entire industry does though. Imagine if you needed an application running in the background for every peripheral you have, for your monitor, for your GPU, for running a hotspot on your smartphone over USB. Imagine having to install a piece of software to access a thumb drive. And that all those applications also needed user accounts. That is the entire point of having drivers.
Microsoft has a new API with GameInput that addresses this situation and allows mapping Generic HID devices onto game controller via config file, but it doesn't work retroactively, it only works for games that use the new GameInput API.
Valve could of course provide a way to switch and emulate other protocols too, just like other third party vendors do, but there is no USB standard that makes things "just work" in Windows when it comes to gamepads, you always need extra drivers, USB modes or other hacks.
On consoles the situation is even worse, modern consoles deliberately lock out any unlicensed third party controller. Playstation3 was the first and last console that supported standard USB controller, while PS5 doesn't even support PS4 controller.
That's exactly how you create a walled garden. You build a garden. Get people in. Then wall it up.
If all the games respected HID and Valve did something proprietary, I would understand the skepticism. The truth is that most games are engineered with platform integration (e.g. for achievements, controller mapping, etc.), and fallback to the Xbox API. It's reasonable for Valve to sell a controller that takes full advantage of their platform.
Also, Valve's primary OS is Linux-based. There's surely either already a module upstream in the kernel or one is coming soon. That is: open source software to take full advantage of this controller. That's not the same thing as a walled garden.
FWIW, it appears Valve is sponsoring development now. Vicki, one of the maintainers of the SteamOS kernel, is the most recent contributor to https://github.com/torvalds/linux/blob/master/drivers/hid/hi...
It's too annoying to search more recent linux-input submissions to see if anything has been pushed upstream yet specific to the new controller.