I'm not sure if you're right or not as I haven't noticed that but his numbers overall have been horrible since April. OPS well under .600 and just 4 extra base hits since then. If he wasn't a chubby, lovable character Twins fans would have been screaming for him to be cut a long time ago.
I don't disagree, but Castro is hitting ~.150 since the All-Star break. You're going to want a 3rd catcher to allow for him to be PH hit for if necessary. Frankly you could argue not having Castro on the post-season roster as I expect Garver to start every game if healthy. But I doubt Rocco will do that.