Earlier quoted context omitted.
For what it's worth, whenever I tunneled X over a non-local SSH connection, it was slow as molasses. That's because almost all contemporary GUI applications render to a bitmap anyway. Those that actually use the outdated X vector graphics operations look like utter garbage compared to anything post-1995. Frankly, I'd rather my applications are at least somewhat aesthetically pleasing.
I routinely use modern X applications running on a remote (25 miles) machine, all day long as part of my job. It works flawlessly if you have a reasonable amount of bandwidth and reasonable latency. Sure, it doesn’t work over dial-up.
That's the point, X's claimed advantages here long since stopped existing, and nobody noticed because the "inferior" approach is perfectly fine with modern internet connectivity.