I think the nature of the fediverse ends up serving as a barrier to entry to the "average" social media user. This is probably why Mastodon hasn't replaced Twitter despite all the dumb things that they have done with the site. As much as people dislike the idea of gatekeeping, I think a moderate amount is necessary to prevent a lot of low effort content that gets promoted on other platforms.

As someone who has been on Reddit for the past 10 years or so, I noticed a dip in quality of r/all and a change in the community when new Reddit came out. Probably because the UI of new Reddit seemed to be geared toward a "feed" style of content consumption, similar to FB or Twitter, so people from those platforms started joining in large numbers and changing the culture. It seems like the recent migration/exodus from Reddit comes mainly from old.reddit users who value discussion and the "forum" style more (new.reddit users probably don't care about 3rd party apps since they just use the official app anyway), so hopefully the quality of content and discussions doesn't suffer too much.