Someone who even knows what the fediverse is and then has enough of an opinion on it that they consider it to be "dead" lies within an extremely niche, chronically online demographic. Best to pay those people no heed whatsoever.

I've met a whole bunch of people in Portland, OR who are on Mastodon, there's even a whole meetup of just fediverse folks. I can assure you, these people are very much alive. 😂