I think that’s a bit of an overreaction. the internet at large has many domains. domains are owned (publicly) by corps - filtering would be pretty easy. I also don’t see any benefit for facebook to behave this way. Facebook doesn’t need the fediverse - most of their users already think of them as “the internet”. Facebook has already taken over the internet (and they really haven’t, as it’s very possible to avoid them).
The internet has always been decentralized. It will always be decentralized. Your attention dictates the amount of control the companies you give attention to have power over you.