Would he only pitch against the AL East? The guy is solid, not great. He has been successful in both leagues. You have compared him to a bunch of injured old guys. The ERA differential between the two leagues is not that great. That's the key stat. Arroyo would be able to hold down a spot with about the same success in the AL. Have you seen the Orioles rotation or the White Sox. Arroyo could do just fine with them.
I find it interesting how so many members swallow their tongues when it is pointed out that the Wily Mo trade was just an awful mistake. The discussion becomes a debate over whether Arroyo sucks and if he could pitch in the AL East. It doesn't address the issue that the trade was a colossal failure. Wily Mo flopped completely. He doesn't even play in the majors anymore. Arroyo on the other hand has had a fair amount of success. This cannot be denied. Whether he could continue to be successful in Fenway is irrelevant. He has been successful elsewhere in the majors while Wily Mo flopped everywhere. The point is that it was a terribly bad trade. They should have gotten a lot more for Arroyo. People can argue the point all they want, but the Arroyo-Wily Mo trade goes on the negative side of the ledger for the FO.