> The churn is largely opt-in.

It is not. React 18 changed damn near everything. You can't create a new React 17 project without jumping through serious hoops. React 19.5 introduced the compiler, so you can stop using useCallback and useMemo. Except for "common scenarios" where you still need it. Which are about as clear as mud.

I can only imagine what React 20 is going to introduce.