The original creators can sure try, but since Lemmy is ACTUALLY open source, the community can just fork the source, call it "the-good-lemmy" or whatever, and devote our time & resources to it instead of using the bullshit version
No. The API debacle was fundamentally about money, after all. In the very unlikely event someone does something similarly one-sided and stupid with a fediverse offering, people will simply fork it or move to different ActivityPub compliant software. Neither is possible on Reddit, a proprietary, for-profit website.
I stand (partly) corrected, then. Apparently not all of it was (and it stopped being so long before it would've been relevant), but still, didn't even know that.
It's not truly decentralized, it's federated. So if lemmy devs change things, each instance can choose whether to pull those in or continue with its current version, potentially defederating as necessary.
This was asked before, but it is under the AGPL (which means that if you modify the code you must make the modifications public), to make it a closed source project you would have to get the agreement of every contributor or rewrite it's code which is very hard to do (and i don't think i ever heard something like this happened). The federated aspect is another line of defense.