Wouldn't worry me (the athleticism thing) because he isn't going to be playing as a defensive midfielder or a destroyer, he'll be there to dictate the play. The defensive side of things will come down to the legs which are put in midfield around him. I guess that's why I said that him and Gundo compliment each other so well. That's exactly Gundogan's game, getting up and down the pitch, making telling tackles and interceptions.
What's the point in having a player, any player, not necessarily Kroos who isn't going to contribute defensively but also isn't going to get goals or assists? You might as well have another attacking player in there. Possession and control don't win games, goals do.