Yes it's the team as a whole and not only 1 position. Busquets was great, but they didn't counter as well in Spain and that Barca midfield as a whole kept the ball extremely well. When Pep went to Bayern he mentioned how good German teams were at counter attacks. So he played Alonso as the #6, but came up with the inverted fullback to help stop it. This is something in which Zinch and Delph helped in that they both sat in midfield along side the #6. Zinch has been terrific, but like we saw on the goal on Sat. he can get caught out and isn't blessed with pace.
Rodri's passing and recycling of the ball is important so you need someone in the squad that can do his job, but you also need a capable fullback that has a mixture of good ball control and pace to slot into the midfield next to him to act like a DM on counters and quick transitions. This was the hope with Cancelo because he has a lot of these traits. That's why he's been a LB with Walker on the right at times. However, he can have lapses in concentration and is better on the right. Hopefully Pep knows what players he'll need to keep the team ticking.