Shocked Pikachu face meme.
The best way to fight it is to simply be unmarketable as a community. This is how Verizon ended up having to sell Tumblr for less than 1% of the price they paid for it like only 3 years later. If the cost outweighs the benefit, fewer people will bother trying.
Have it as a distributed network of smaller instances, rather then having everyone pile on to 2 or 3 big ones. It’s easier for admins to notice the bots if their site populations remain relatively small, and it’s easier to defederate from sites that are enabling the bots if they’re not also home to 80% of users.