I remember how stagnant it was before EGCS came along, that's how old I am. :) EGCS was clearly technically superior to GCC (at least in some ways), and when the FSF gave up or came to its senses then the EGCS and mainline GCC projects were re-merged. (Compare also the Rails/Merb fork/re-merge.) By contrast, no-one outside Canonical seems convinced that Mir has important technical advantages over Wayland, and (as far as I've heard) Canonical seems to have little interest in preventing or minimising balkanisation, so it's hard to see the justification. The more efficient way for Canonical to speed up or shake up Wayland would seem to be to contribute to it, or failing that to maintain a fork designed to be a candidate for full or partial re-merging, no?

(I am not an expert on anything.)

gcc is not a standard though, it's a product. It's a bit different in this case and I totally agree with you.

GCC wasn't stagnant at all. There were relatively frequent major releases including ports to additional platforms, very good progress implementing stuff like C++11, better optimizations, and many other important improvements.

Clang has helped show some additional areas where GCC could perhaps be improved, but GCC was surely not "stagnant" at the time. It wasn't like during the EGCS situation in the 1990s.