Everyone online community can be perfect if group membership is small enough. Up until that point the underlying tech does not matter. I have been part of great hobby groups and discussions on niche subreddits, random Whatsapp groups, Usenet/IRC, even plain old email threads. So in that sense, yes, Mastadon can be great as well.

The real test is – can your community handle an influx of a billion of the worst users on the internet? People baiting for flame wars, bots, scammers, pedophiles. They are all out there, and will show up the second your service has a whiff of popularity.