Different sport, but I got paired up with an NBA ref a couple of years ago golfing. Very interesting perspectives - they do have a ranking system and the bottom 25% (I don’t remember the exact number) are put in watch for being replaced. This ref hated that. He was basing it on the idea that there was a high standard just to get the job, and not a huge amount of variation in their metrics from best to worst.
I think baseball has more variation, plus is more possible to use technology, though.