I am not an analytic guru but Contreras has always seemed like a fine defensive catcher to me. He is big, athletic, and has a very strong arm. Perhaps he gets dinged for pitch framing and how he calls a game. I don’t know. From what I have read Molina endorsed Contreras for the job and Yadi knows a little bit about the position.
As for Knizner, it makes sense that they are just trying to light a fire under him. Thus far his career has been a bit underwhelming. He has gone from heir apparent to trying to hang on to the backup job. He is fine for starting once a week but I wonder who the Cardinals would go with if Contreras happened to sustain a long term injury?