You're forgetting something important here... Being a regista is not only about the position one can play, it's about being the one that dictates the flow of the match, the one to have a team built around him, being the main target from teammates when looking for offensive plays. When you take that into consideration you'll see the names you mentioned are far from that, with the exception of maybe Sahin (And Modric, but he didn't really impress me at Madrid. Liked him better as a CM/AM at Tottenham). Oh and btw Schweinsteiger is a box-to-box mid. Gundogan is a top player but don't know if he'd be able to fit Pirlo's role.