Im joining in on the reddit ditching thing, and was kinda worried at first that i wouldnt be able to like use it the way i did reddit as it feels like a whole new place, but after engaging with posts and people and actually being a part of lemmy rather than being lurk mode all the time i was pleasantly surprised with how easy it is to become a member of the community, theres a reasonable amount of subs (or whatever the other word for em is) that fit my interests, enough linux content and shitposting for my liking, and the overall random posts made by people equally fed up with Leddit. (also i admit i used reddit a little cus there was this post on the fedora sub showing how to fix a sound issue i been having after a recent update)
Bonus for Lemmy being federated, though - if lemmy.world or lemmy.ml no longer gives users want they’re looking for, you can start your own flangscrawchl.er and choose whether or not you want to federate with them.
Corporations will have their own draw; shittification is a thing they do after they have majority market share and their users are entrenched. A new social network service could rise (even one made by Google for Facebook) that is easy to use, has QoL features that network it with its corporate siblings, etc. It sees increased traffic, it gets big… then it shittifies again.
As long as users are following corporate interests, this cycle continues. It’s a slow-burn likeness of competing ISP sign-up contracts throwing in Xboxes. (Though I hear the US has service deserts, so that mightn’t happen there.)
Lemmy probably won’t shittify to the same degree; while larger servers like Lemmy.ml can house a huge percentage of Lemmy users, it can’t ‘go rogue’ in a way that means anything to Lemmy as a whole.
It also can’t offer the same QoL features a corporatized service can, because those can afford to operate at a loss while building market share. A subsidiary can be used as a ‘loss leader’, ie: it doesn’t matter if it costs more to run than it earns directly, because it gets users into the door for things that do profit.
What you describe can, and mostly likely will happen. But Lemmy’s nature makes it more responsive to user interests.