Yeah. It's going to be subjective based on whatever criteria is used. The league I have the most fun in where I consider my competition to be the most knowledgeable will probably finish much further behind publicly lauded leagues that don't really impress me as far as knowledge or talent.
Parity doesn't mean anything, honestly. To me it shows less owners who have it figured out, or have an organizational plan. Consistency should be more praised than cycles of failure and success.
Retention is difficult to gauge because some owners, as MikeT said, are kicked out for poor performance. And I've seen that in the longer-running worlds, it's much more difficult to replace a team with an owner committed long term. I think more people are gravitating to more untainted reclamation projects or something that might be easier. Usually it's the same franchises that lose their owners, and that says more to me about a lack of good owners available than a world's capability.