Its clear Pep has realised that de-bruyne in that center mid role had been struggling these past couple of months so moving him to the wing is not a bad idea as he has better delivery than sterling. I guess the problem with him instead of sterling is that you will have no penetrating runs in behind that arsenal defence which would've especially been useful on a pitch as wide and big as wembley but I think pep's hoping for navas to provide that width. A bit unfortunate for sterling to be dropped 2 games in a row after a man of the match performance against hull city but I'm actually fine with that team and he's always on the bench if needed