His arm isn't bad. He just has no movement back there. He looks extremely awkward with ball in the dirt. He doesn't slide side to side with ease. He looks like a bulldozer behind the plate. I would totally would not trust him to block any kind of nasty slide or split in the dirt.
Speaking of catchers, this is why Welli should have never been tossed aside. Since he got traded to the Dbacks..
.284 AVG, ..363 OBP, .543 SLG, .903 OPS, 143 OPS+ in 91PA. Also, has 5 homers and 15 RBI's in that span. We traded him for pennies because Lester wanted Ross. Now, we have no catcher and a offense desperate for offense. We all know Castillo is a great defender behind the plate. His down fall is pitch framing which I am still not sure how much you can validate that stat considering the umps have a lot to do with the zone that is being called.
Sometimes I think Theo and them value there old players way to much and like to cast aside other players. Dbacks essentially got two prospects, salary dump, and a starting catcher for Montero. They made out pretty good.