You seem to be implying that it's nigh-impossible to write games that can reliably run at 90+ FPS and no dropped frames with a game engine because the game scripting logic runs in an interpreter with garbage collection
It's definitely worth being careful to avoid GC causing frame drops, but I'm pretty sure there are a lot of good-performing VR games written in Unity
Unity is a over-engineered pile of &%$#. And now I'm being too nice.
And it's getting worse by the day.
The company is bankrupt, and when interest rates go up further all your invested time will go poof in a second.
Own your time, and control your future: when you use Unity you learn very little about how the GPU works, which kinda is the point, but since OpenGL 3 is the final 3D interface with VAO you only need to learn it once for eternity.
It's definitely worth being careful to avoid GC causing frame drops, but I'm pretty sure there are a lot of good-performing VR games written in Unity