The current formation seems to be 4-2-1-2 Messi. Rakitic plays alongside Busquets, with Arthur further upfield pretty much in the center. Rakitic does go forward sometimes, Busquets never does, but both defend a lot more than Arthur.
Look, Rakitic is going to play a lot. He does on every team, for every manager. You can certainly appreciate what he does by seeing what the team lacks when he is not on the field. The team deteriorates even more when Busquets is not on the field.
Both Rakitic and Busquets need to be rotated more, so it is essential for someone to prove he can cover for these two. I don't care who. Roberto has not looked like he can do it far this season, so surely Vidal has to be given his shot.