All stats have flaws, but most stats, even flawed ones, have useful information.
I like CERA--or even moonslav's OPS against--as a way of looking at how well catchers handle pitchers because I emphatically believe what Mike Mussina reportedly said: pitchers often struggle because that don't have their best stuff or good command or both in every game.
Thus, no matter what the game plan for going after opposing hitters may say, the pitcher and catcher must improvise based on what that pitcher has that day. And that especially applies to this season when pitchers suddenly have to deal with not doctoring up the baseball to get more spin/action/movement on their pitches.
Thus it is interesting to me that this year Vazquez was Eovaldi's primary catcher before the Commish's dictum hit MLB in June and that Plawecki and Wong have caught Eovaldi more than Vazquez after the dictum.
On the other hand, it sure looks as though Vazquez is the right guy to catch ERod, and maybe Plawecki is better with Pivetta.
As for Perez and Richards, I don't care because they both stink.
So right now I'm thinking the tiebreaker is that Vazquez is better with the bullpen, and the bullpen has saved the Sox ass innumerable times this year. Plus all that stuff about better mechanics, arm strength, whatever.
My cautionary note, however, is that the bullpen has stunk for 3 straight games, and in 2 of those games Vazquez was catching when Cora brought in his best relievers, all of whom were pounded. In the 3d game, last night, Plawecki did a great job with Eovaldi and Rios, but lousy with Valdez--but also with an insurmountable 20-1 lead.
Bottom line, regardless of CERA or any other stat: Cora knows what he is doing and prefers Vazquez. That said, my guess is Plawecki, catching every 5th game, will continue to catch Eovaldi.