You're absolutely right and the fans should be grateful for both of them for bringing us back to where we belong.
I am not putting the blame on Allegri for our CL recent failures but what I am trying to say here is that we have been losing in the champions league due to our game mentality which no Juve manager (and they were many) has ever had the guts to change or revolutionize, like Sarri is doing with Napoli.
That's why I think this decision has to come from the club management (Agnelli and co), try something different. When you have players like Costa, Cuadrado, Dybala... you might have a chance of playing differently.