So, this is just my opinion, to clarify. And I'm sorry if anything here comes off as harsh/angry tone... it is not my intention to provoke anyone.
I personally think that people's standards for Fandom are too high. And... I'm not really surprised. But Fandom has mentioned that UCP isn't perfect, and people seem to ignore that. Instead of promoting changes that you think would be beneficial, you assume that they would've "known better" and straight up leave. I don't really see how this helps Fandom change for the better, if anything, it makes it worse.
Do you remember the days when people were mad that Fandom made message walls? Well, they were in the exact same situation as we are in now. People leaving, people complaining, etc. And now, while there are still people who prefer talk pages over message walls (I'm not saying that's bad), they aren't complaining at all. I know that the situation with UCP is much bigger than the situation about message walls, but I feel as if they are comparable in some sense.
If I'm being completely honest, I'm not the biggest fan of the new editor, too. I preferred a lot of things in the old editor. But I'm not gonna pack my bags and leave Fandom, because I think it would be better for me to report bugs and suggest changes about UCP to Fandom themselves, so they can make it much better for everyone. I suggest that people start doing that, too.
Edit: I edited this post to give it a less harsh/angry tone and instead a more gentle tone. I'm sorry if anything in the previous post was too harsh.