How convoluted the protocol is doesn't really matter as long as someone creates an easy tool to spin up your own server.

I think the XMPP comparison stills stands: Google was able to steer how the protocol developed, or which version of the protocol people used because they had the majority of the users and other servers wanted to still be able to interact with them.

Suppose that Facebook joins the fediverse and most large instances federate with them. All is great, then Facebook starts to make demands to other instances in order to keep federating with them, e.g. no posts about protests. Because a large share of ActivityPub activity will be on Threads, naive users would prefer instances that federate with it, so instance mods will be incentivized to comply with Facebook's demands to attract new users and maintain their current one and... you see where this is going. The only way to deal with this is to deny Facebook this kind of leverage in the first place, either by blocking them instantly or at their first mishap or demand.