Looking through VaM code I wonder if there is even a need for unity lol. Unity seems to just be for running mono, displaying UI, keeping a list of game objects, forwarding positions to physx and starting rendering. Everything else was written by @meshedvr from scratch.
You are not entirely wrong, and VaM2 will be similar in some regards. I do very much rely on things like Unity's asset management, UI system, VR integration, and rendering system. But where Unity fails, I'm try to go further. Part of what made VaM different than others is I didn't rely completely on Unity. I had to do a lot of stuff myself to push the limits of what was possible (within this game engine and C#). I do know it could be better not relying on Unity and C#, but that was not something I could really take on at the time, or even now. Unity's improvement with c#/jobs/burst has me convinced I can eek out a lot more from the engine than previously. I can also get around Physx limitations with custom written physics where needed.