Depends on the latency which is the achilles heel of 9p and plan 9 in general. With 9p, for every T message there's an R message that is waited on before the next T is sent. So if there's 100ms of latency you have to wait 100ms between EVERY 9p message. Pain and suffering. The labs people never focused on performance but actually building a clean comprehensive system with the small team they had. It was a pragmatic approach for sure and compromises were made.

Though when using local ethernet, heavy graphics isn't that bad. I can play doom over local ethernet using drawterm to a cpu server which is actually running the doom processes. Of course blowing up the game screen makes it suffer as doom doesn't use dev draw.

Another thing to realize is that plan 9 graphics are done via dev draw which is a sort of 2d graphics engine that you load text and bitmaps into then issue commands to draw and move them around on screen. So a local dev draw on the terminal only receives draw commands for the loaded resources so there is some caching and heavy lifting done at the terminal end. It's not like vnc or rdp where you are viewing a remote frame buffer.