Astudillo just has an adjustment to make. He came up and hit everything. So pitchers adjusted by throwing out of the strike zone knowing they probably won't walk him. If he adds a little patience to his approach, or if you just give him some take signs in early counts, he'd get more hitter's counts and the adjustment is likely made. That's a realistic possibility.
I don't think Baldelli considers him a third catcher as much as he considers him a utility guy that's willing to put on the gear. Also a catcher getting hurt and needing an IL stint or just a few days off is a likely scenario. A player like Astudillo takes the pressure off a catcher to play hurt. Then consider his contact skills in a game where players are striking out more than ever. That's very valuable to a manager.
I would hit him lower in the lineup, but Baldelli's going to be slow to send him down. It's easy to see why.
I agree with all that was written above with the exception of that Baldelli considers him a utility guy that's will to put on the gear. Astudillo got starts when both of the other catchers were healthy. To me, that indicates he is regarded as part of the catching rotation. With his bat cooling, I doubt Willians gets many starts behind the dish in the immediate future. He would be the candidate to be optioned if there is a need for an additional relief pitcher.