

Not as comprehensive as Facebook Groups.
Facebook strength is having big community from Asia and Africa. While fediverse is mostly Westerner (and isolated Japanese). Unless people from those continents move here in huge wave, I don’t think Facebook will get replaced.
Mastodon is not valid recommendation for them, as these people doesn’t even use Twitter or even hates them.
Any social media technically host the same variation of people. It can be good or bad depends of your social circle and what kind of people you follow. Even fediverse has its own bubble of hostile people.