While it is true that 3/5 of the rotation is shaky, there is no definite spot in the rotation that getting a top pitcher would be a huge upgrade over. Hill and Marshall both have the potential to struggle or pitch well over the rest of the season, and though Marquis is unlikely to be as lucky as he was in the first half, he isn't as great a weakness as SS, C, RF, and CF. There is a chance one of the three has a complete meltdown during the second half, but there is very little chance we will get any production from several positions. That's why the team needs a bat more than a starter.