Haven't considered the wall hacks, that's a good point. Still though, I think you could mitigate this with a few different techniques. The CPU cost is largely

Haven't considered the wall hacks, that's a good point. Still though, I think you could mitigate this with a few different techniques. The CPU cost is largely there anyways, as you are updating everything on the client from the server anyways. Any games that rely more heavily on physics will have more work to do to simulate yes, although basic gravity/velocity calculations with some linear interpolations thrown in is very lightweight, even when talking about 100 players. Bandwidth is quite small, how much data does it take to send a single key stroke? A number of bytes really, multiply by 100 players, multiply by say 2 or 3 keystrokes at the same time, multiply by 60 frames per second, and you still get a very reasonable (dare I say negligible?) amount of bandwidth. The point is not for it to be authoritative whatsoever, the point is to not have to wait on two round trips from the server to get location data from your opponents, but try to do it in one round trip. If your connection to your opponent is lower latency/more stable if done through the server, then that should be the fallback of course. Movement prediction/smoothing happens even to your own personal character, even on a good, low ping connection to the server, the good games just know how to hide it effectively, but you often still get people complaining about hit registration. There is no perfect model outside of everyone having amazing internet connections.