Meta (or any large entity) cannot monopolize or control the fediverse. If their implementation starts drifting from established norms, they will be blocked by most instances or will just be incompatible. The example used to back up this argument is usually XMPP, but people forget that XMPP is still around. It never died; its just a smaller, niche network.
The fediverse is already a small, niche network. So if Meta comes in and tries to control the network, it will then be responsible for maintaining its own "Meta-fediverse" network (that some instances may choose to be a part of) while the remaining instances will remain as a small, niche network. Meta can't force current fediverse servers to implement any Meta-specific features or to change their software in any way.
The mod workload argument is the only one that I see being a real issue, but the target is wrong. Anyone worried about that should be discussing it with fediverse devs to improve mod tools, not trying to force the entire fediverse to stay at their preferred size