I think there are a number of things in play here

A) Pep has raised the standards so much in England it is incredible. You really need to be one heck of tactician to coach in that league in my view. Smaller clubs like Brighton even have savvy tacticians at the helm.

The extent at which things have changed can even be witnessed in lower leagues. City were playing a League 2 side a week ago and they were trying to play from the back against City. Pretty much everybody is trying to play from the back now largely becomes of Pep.

B) You touched on this is your second paragraph. Supposedly, there is a lot of infighting at the club. Benitez appears to be some kind of strange politician type who turns people against each other. He of course also got the Director of Football fired.

C) I also think he is a bit like Mourniho in that the game has kinda passed him by.