Instance picking can be overwhelming. Making people just not even try it.
I do think a big challenge for the fediverse is how to ease that. And make it like e-mail where @whocares is not that important and it's easy to actually have a custom domain/instance.
And, of course, to achieve this instance admins should be really be responsible with defederations and bans. And only use it as last resort, probably only because of legal reasons. Not because "I don't like that instance admins main political thesis". Probably that kind of blocks are better to be left to the user.
that's not a bad idea at all. much more beginner friendly to download an app and register from there rather than having to do it externally and then coming back to the app to log in