Chromium and AOSP are not good examples for what you’re saying. Both Chromium and Android have thriving ecosystems of forks and alternatives based on them. Built on the work that Google is doing with them. So I really don’t think those are good examples of applications that aren’t healthy because you can just use a fork.
Yes, Google controls upstream, but there’s no reason why you can’t use downstream.As you said, it puts maintenance burden on the forks, but people are willing to do that. That’s the thing.
EDIT: This is my off account, So, unfortunately, you’ll have to take my word for it, but I did used to be part of an Android ROM team in the past and still do Android work private sector today.