I can tell you what my problem with Mastodon was.
"This looks interesting. What web site do I go to to sign up and start using this? Huh, there are unnecessary hoops to jump through. I can't be bothered with this right now. Maybe I'll look into this again later."
And later never came.
If understanding what the fediverse is and why the whole point is the diversity of servers, then you're not ready to discover the fediverse.
It's not a bad thing in itself. The fediverse is not just another service, another app, another social network. It's a way to organize together as a society, as a group of humans. It might take time to understand how it works, but it's worth it.
I think she has a valid point that it's often misleading to refer to "the fediverse" as a holistic thing when it's really a network of wildly different small communities. However, you could say the same about Twitter or Tumblr or HN or New York City or really any social place above a certain size.
I honestly haven't understood at all what the problem with Mastodon was. If anyone could explain this, I'd be grateful.