Busquets seems to be a polarizing figure, and I think each has valid points.
He is the most cerebral, disciplined and skilled CDM in the world. However he also is a little bit slow and lacks some aggression/physicality.
I think in he right grouping he can be part of the best midfield in the world, but in the wrong group he can contribute to our midfield being overrun/out-physicalled. I think that is why bringing on complimentary players is vital. Busquets, Rakitic and Coutinho only make a world class midfield if you add a 4th midfielder who is athletically imposing box to box type in the mix 4-4-2 OR you in a 4-3-3 where two of the forwards also work their butts off defensively (like Suarez and Neymar did in the most recent treble season).
This additional dynamic was not available to the team last year. Sergio Roberto in the midfield is not this player. Rafinha is not this player (though I think it would be wise to keep him--I like him a lot better than Denis or Gomes and he is more proven than Arthur).
I was excited about the discussion on moves for Kante, Pogba, Rabiot and Savic-Milinovic to compliment some lacking elements to our midfield options (people forget the trouble Pogba caused us in the CL final and you saw for France how disruptive he can be to opponents. However I am sure all proved too expensive/impossible (would like a run at Saul too but with 150 mil release clause just not plausible). And that is where plan B came in, exploring Pareja, NZonzi and then springing for Vidal. If Vidal is 90% of what he was he is definetly the best of this plan B group and a better all around player than Paulihno, the latter with a lot more flaws in composure on the ball, quick touches and passing/vision.
However the addition of Vidal (if a 4-5-2 is still used) AND Malcomb may be a great compliment to Busquets/Rakitic/Countinho core (if we use the 4-3-3 it will be clear Dembele or Malcomb would have to work their butts off defensively or the other guy gets the place). Vidal is a champions league elimination round signing pure and simple (OK maybe needed for the Classico and vs Atletico as well). I like it.