The problem with this reasoning is that many of the popular communities are actually on lemmy.ml, and they're not so easy to replace. I mean, in terms of content and engagement lemmy is already a pretty small place as it is.
I think this is a core problem of lemmy as it is right now. This place is meant to be federated and decentralized. Instead it is heavily centralized as communities lie on one instance. What one needs should be federated communities as well. Like say c/linux@lemmy.world is the same as c/linux@someotherinstance.com. this way one could subscribe to communities on your home instance and if the home instance defederates from one other instance the community can defederate from the community on that instance without completely breaking apart
What I mean is that a subset of all Linux communities agrees on a common set of rules and forms a community of communities. Content of all communities is shared with everyone who subscribes to one of the communities. Every community moderates its own content. If one community decides to have stricter rules than the others it can defederate. Basically just like on the level of instances.
What stops us to just defederate from lemmy.ml is that the community is hosted there and all members are linked to that one point of failure.