I'm not doubting that Schweinsteiger has been the better player over his career, but stats aren't everything either.
http://eplreview.com/statistics-topassists.htm#EPL2014-15TopAssists
This has Chris Brunt on 9 assists with the likes of Ozil, Coutinho and Mata on 4 and 5. Doesn't make Brunt the better player.
McCarthy's game is about more than assists and goals. You don't get stats points for preventing goals with tracking back etc and sensing danger. I'd say McCarthy is up there with the best of them for doing that. That's just one aspect of his game where he is very good.