I think there's a good mechanism to keep that from happening given that you can always just spin up your own instance or join a different one and still be federated with every other instance of interest.

That current state of affairs (people having content on a multitude of instances) should keep that from happening, since a bad actor would need to capture sufficient content as to have the only instance worth visiting.

I can't foresee myself years from now having a problem making a new account on some-new-lemmy.place in under 3 minutes and continuing on my merry way.

Or at least that's how it seems to me.