If you go through the changelog, v13 as a release is mostly about improving existing features but I don't think pg is at that point yet where it could "stop" adding features. It almost stopped 8-10 years back and that is when mysql had overtaken it completely. I believe it still is the best open source SQL engine but features like native partitioning, JSON support etc that have been added in the last few years were absolutely needed in this century to be competitive. And now that they're there, they need to be improved and made stable.
