How does federation solve the problem of powermods?

It’s possible to become a mod for a remote community outside your instance. I don’t think anything technical about lemmy or the fediverse prohibits someone from attempting to become a powermod by founding or offering to help moderate many lemmy communities. I’d hope it doesn’t happen again just from the knowledge of how it worked out last time, and that existing mods would refuse to take on mods with an excessive list of existing communities they moderate. But I don’t see how federation structurally prevents it from happening again.