Not in what concerns graphics rendering performance.
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.
This is entirely false.
The 9P protocol is asynchronous, can handle up to 16k outstanding requests, supports out-of-order responses, and includes support for arbitrary request cancellation,
The only thing thing that blocks to wait for an R message are blocking syscalls, but that doesn't stop other processes from sending further T messages.
But this is the reason why drawterm or rcpu is not very usable over high latency connections.
The simple draw commands issued by Plan9 applications over /dev/draw by e.g. acme or rio shouldn't be cause for concern.
There is no accelerated graphics here, nor UIs that need it.
Acme and Rio are simple because they should be, not because they couldn't be anything else.
Although, you are correct that UIs have degraded extremely in tandem with the increase in available resources, which is very frustrating.
