Sure, but like I've said, you can't reasonably give all the credit to Mourinho. Di Mateo's side, for example, allowed amongst the least goals in CL group stages, they kept Barca quiet in the semis at home, they managed to draw away while playing 60 minutes with 10 men, and only allowed one goal in 120 minutes of being absolutely battered by Heynckes Bayern. And that's what, 4 years ago? They've been doing that **** for a long time now.
And its the backline that really makes or breaks playing in that style. Terry may have mobility of Stephen Hawking, but he's still the best out there when defending with deep line. Similarily, Cahill may **** himself everytime he has to step outside of the box, but put him 5 meters from his own post and he turns into Georgio Cahillini, Destroyer of Dreams.
Mourinho without a doubt is the best defensive manager out there, but he didn't turn Chelsea into the best defensive formation. They already were that when he arrived.
It can be reasonably argued that a lot of what he did in his first spell at the club actually contributed towards players such as Terry's development which stuck till now. Although I broadly agree with the general consensus, Mourinho is a great defensive manager but their are other managers too who can hold their own