Corporations don’t just sit out on new technologies, and no matter how hard you try you can’t force them to. Defederating from Meta’s new project preemptively is naive, and will not do much of anything.
Protocols are going to be adopted by corporations, whether we like it or not. SMTP, LDAP, HTTP, IP and 802.11 are all examples of that. If it ends up that meta is able to destroy the fediverse simply by joining it, that is a design flaw on OUR end. Something would then clearly need to be different in order to prevent future abuse of the protocol.
FOSS is propped up by corporations. By for profit corporations. If you want to stop those corporations from killing projects, you put safety guards up to make sure that doesn’t happen. You don’t just shut them out and put your head in the sand.
There’s nothing wrong with being a separate entity from big corporates. Mastodon is pretty big already and it’s going keep growing. Fast growth isn’t the point, it’s sustainability and providing a haven for people who don’t want enshittification and other corporate bullshit. If someone want that they can just use a corporate owned social media, nothing wrong with that. Reddit has never been the biggest fish in the pond anyway, and the whole thing with trying to pull in users is a part of what made the platform worse. Bringing in corporates is gutting the biggest thing that make Fediverse appealing. And for the record, there isn’t that many big companies that’d be a threat anyway. Any corporates that aren’t big social media corps isn’t really the problem. If Nintendo wants to make an instance to be the second Mii verse I highly doubt many people would be against federating with them.