I believe this argument is slightly weak. I understand that the ecosystem is very diverse but even on Windows most new games only officially support Windows 10. If you're on 7 for any reason then it's your problem if the game doesn't work. Similarly if you're willing to go down the Linux route developing and deploying only on Ubuntu, for instance, can be regarded as a "single platform". It's my prerogative to use whatever I want on my Linux box but then it's my problem to make sure I have all the required components available for my bespoke setup. I haven't used Ubuntu in years but give me a "Ubuntu executable" and I'll find a way to make it work on my desktop. And if you don't want to limit yourself on Ubuntu Valve is now rolling out their "steam runtime containers" which are reproducible environments for developers to target.

There are still issues with the drivers, I'll give you that. But at least AMD/Mesa is moving fast to adopt features. NVIDIA is going to be NVIDIA but at least they are not skimping on implementing OpenGL and Vulkan extensions.