Let's face it until we build for a 4-2-3-1/4-3-3 (There are others but these 2 are the most obvious ones) we'll have $#@! width and a huge weakness. I don't care if you have 9 World Class players in a narrow at $#@! formation, you can still be abused on the flanks. But, of course we don't, so yeah.
This is also due to a lack of real threats at the full backs.
But you know, with this very squad Allegri could and should have given a go to test a 4312 with Marchisio - Vidal - Pogba / Tevez / Coman - Morata.
Tevez has the required characteristics for a trequartista if he's willing to let the ball go. He's got the vision and the passing. Coman would go through the lanes and Morata a mobile CF, sometimes at the lanes for Tevez and the mids to get into the area for the finish. This would be a very fast and dangerous team. If Coman had more opportunities during the season he might actually be considered for this. Also use Padoin as a left back who provides good defensive cover, and unleashes Litch to go up more at the right.
With our players, the formation that suits Europe best would be some sort of 3-3-3-1 with the ball, similar to Bayern:
------------------------------Buffon-------------------
-----------Bonucci -----------Chiellini ----------------Padoin
------------------------------Marchisio-------------------
----------Vidal--------------------------------Pogba-------
Litch-------------------Tevez--------------------Coman
---------------------Morata-----------------------------------
Without the ball, it goes back to a 4312 with Litch as a RB, Coman tracing back at the left flank, Morata tracing back right flank, Tevez marking the middle.
Of course this is impossible now, since it hasn't even ben tried and Coman has no significant playing time. But I really wished this could have been developed by Allegri during the season against weak teams.
This would be a very techinical and fast team, great for the high pressure. Only problem would be Chiellini and Bonucci as slow as they are. Maybe try Caceres for Bonucci. But then we'd have a height problem.
Just pointing out that the width and lack of pace problem could be tried to be solved with the current players we have. Tevez as a trequartista would be the basic solution, inserting a pacey guy in Coman.