You've answered your own question basically.
Mourinho 2.0, Hiddink, Conte, Sarri, Lampard, and Tuchel. 6 managers in 6 years, and we've seen the same lackluster, slow football. Now you need to look at the players who have been here the longest:
(Azpilicueta, Rudiger, Alonso, Kante, Ruben, Kovacic.)
It clearly stems from the personnel. This turgid slow football followed by a collapse in mentality happens every season under a different manager, but these 6 same players are always at the helm of it. I'm sure there are other factors being played, but the personnel is the biggest one. A massive clear out is needed.