Oh, wow, thanks for that pointer to InstantSpaceSwitcher - looks like it might help with my biggest annoyance.

I have "reduced motion" switched on, so don't get the animated transition - instead there's a brief fade, followed by a few seconds where any input is silently ignored. So, if anything, it's even shoddier.

Honestly, the modern MacOS experience feels slightly worse than Linux from 20 years ago.