Biggest fault here is Marotta's. He made the coach job very difficult with his dumb and poor timed decisions last summer.
But Allegri is failling miserably. We lack leadership on and off the pitch.
Against Sassuolo, he failed in playing Mandzukic and not Morata and in replacing Khedira with Sturaro (his lack of skills damage build on, Hernanes should be playing, but it hardly would make a difference).
But mainly, he failed with Cuadrado's positioning. He's playing like a RW, not like a RWB. We got exposed and unbalanced again.
Anyway, championship is off the table. Ability to fight for 3rd position is highly questionable.
They must go for a coach now, and when they find a suitable one (not an easy task), fire Allegri.
And the search must start NOW. There are no signs of improvement on the team short term.