In reply to Steve Grant.

My thoughts too...
I'm constantly busy with fixing stuff, I coded before and now there's a Gutenberg-button for what I had coded and it either overrides my stuff or the button doesn't work. Both is distracting for my clients.
I tried out FSE for a small project but ultimately abandoned the block-theme-approach, because the warning banner was more confusing than did help.
I wish they would give it more time. But it happened with Gutenberg and it will happen with FSE. Merry Christmas! :-) At least, I know, sites will not break with 5.9.