[mellinoe]

In my experience, trying to get OpenGL to behave the same way (and with the same performance) on a bunch of different systems is actually more work than just maintaining multiple backends. Testing OpenGL on Windows does not in any way guarantee that it's going to work on Linux, or macOS, or whatever else -- even if you don't add a crazy OpenGL extension support matrix into the mix. So your QA budget is already going to include testing OpenGL on all those platforms.