Nobody bothers to guess what's the potential of some new graphic card once all drivers, games, OS etc are fully tweaked and optimized. You decide on performance now.
We knew this would happen for everything using Rosetta, that's just part of transitioning to a new CPU architecture. For Vulkan vs Metal that's self-inflicted on Apple's part.
Well it worked for Microsoft
1: https://docs.microsoft.com/en-us/windows/win32/opengl/portin...
These days you're better off using OpenGL via ANGLE, built on top of Direct3D. That will probably also happen analogously on Apple's platform with Metal, so I don't quite get the kvetching about Apple deprecating OpenGL.
As if it matters whether Apple ships an OpenGL implementation as part of the OS or purely as a normal user space library.