I think that some of their points are good. I think the major one is that unless you run your own instance you have no ownership over your identity (save the mastodon migration tools). I think it is weird that if I want to use Mastodon to post short messages and PeerTube to post videos I need two different identities. I think it would have been better if I could have a shared identity that could be used across multiple fediverse apps, or used to move my identity from a "shared" provide to a new one, or a self-hosted one.

I also think that length-limited posts are not a great basis for a social network, but that is not mastodon specific.