You can put the blame on Allegri all you want (and he is to blame for some questionable decisions), but you need to remember his squad consists of only 5 Juve-worthy players (3 injured in Chiesa, Dybala and Danilo) and then a bunch of underwhelming, inconsistent, useless players the likes of Rabiot, Bentancur, Alex Sandro, Bernardeschi, Moise Kean, Morata, MDS, Rugani, Kulusevski etc.
Ironically, the one to blame is a clown in north London. This team will struggle for a long time simply because you cannot replace that number of players in 2-3 transfer windows.