They keep echoing the same worries without actually providing solutions. ... Start proposing changes to protect ActivityPub or just step aside please.

That is a non sequitur. Maybe the doomers are right and AP is simply non-viable in the long run, and the right thing to do is abandon it rather than protect it. That said, I couldn't make much sense of the linked article. I did like the description "51% attack" which I hadn't seen in that context before. It's not exactly accurate but it's a nice metaphor.