[AndrewStephens]

Counterstrike aimbots have done what I describe for decades. They can aim and shoot in one frame, then aim and shoot at someone else as soon as the gun animation allows, exactly like playing against The Flash. The Flash might not be cheating per se, but he would be unsatisfying to play against as he decimates your entire team in a second.

Shadow meshes are often generated by rendering the scenes from the viewpoint of the light sources. This would have to be done on the server, so the server is already doing some rendering.

Sounds certainly need to be rendered, even for non-visible players. Otherwise you couldn't hear someone shooting behind you.

You ideas would work much better with a RTS. But so do solutions like Stadia.