Completely agree. I pushed hard for this to be opt-in before 5.8 was released, but the core development team from Automattic didn’t see it that way.
See conversations on Slack:
https://wordpress.slack.com/archives/C01D71823PB/p1624463727305700
I get that, not wanting to leave people behind. But I’m sure you can appreciate the subtle difference between “not leaving people behind” vs “thrusting a not-yet-wanted feature on someone without their consent”, especially if it has the potential to break things, as this change does.
Therefore, I really feel this should be an opt-in feature. That way, nobody is left behind, and nobody is forced into something when they aren’t ready. When you’re ready, opt-in! Easy.
The block editor has generally been regarded as a great thing (I agree that it is!), but with a terrible rollout that fractured the community, and broke trust.
I think it’s wise to learn from those mistakes, and make massive changes like this opt-in.
Unfortunately, I was not able to have any success with those conversations.
So sorry you had to spend time on this, and I’m glad to hear this plugin helped you.