There's no doubt that he did a great job at Chelsea during that first season, the switch to a back 3 took the league by storm and nearly everybody was caught flatfooted, but next season, when the other teams caught on, and he had a dogshit summer with Morata, Drinkwater and co, they were 30 points behind league winner and 23 points behind their own record the previous season.
Signing mostly Man Utd deadwood doesnt mean anything, players can fail at one club/league and has a great time at another, Robben and Sneijder were deadwood at Real, need I remind you. The fact remains that over those two seasons, he spent the most money in wages and transfers in Serie A. That transformation didn't come at the drop of a hat, and for every Lukaku who found his groove in there, you have a Sanchez who was still adequat at best and a Eriksen who is still in the mud. He is tactically sound and does improve players, but he's no miracle worker.
As I said, I share the frustration of the majority of this forum regarding our manager, but just because ours is terrible doesn't mean its all roses for whoever we decide to put him up against.