Trading your best player in a year where you're one of the best teams in baseball and an obvious World Series contender would be a top 5 dumbest move in the history of baseball level choice.
Busch, PCA, Suzuki, etcs numbers look like they do because of Tucker's presence in the lineup. You take him out and all of a sudden they see far fewer fastballs and anything near the zone. You don't replace a guy that doesn't strike out with a guy with a giant strike out rate for two more homers over the course of 60 games.
As for Caissie, he's probably an overpay for about anybody that's going to be available other than a package that gets you Joe Ryan AND Jhoan Duran.