If Cooper had come back to his regular self in a relatively quick amount of time it would have come off as disingenuous if not preposterous. He spent 25 years in the lodge and then went through an extremely bizarre and terrifying process in order to return. One can only imagine how this would effect him, especially when you take into account his doppelgangers sabotaging of the process which could have only compounded the problem of his return.
I mean, if the journey back to Dale Cooper didn't take a long time it would trivialize everything that happened to him. There has to be a definite weight to the things Coop has experienced, not just with this season but the previous two seasons as well, or else it all falls apart and we lose the Truth that drives the story.
I personally really enjoy perceiving things from the pure eyes of Dougie. Coop greatly admired Annie's pure perspective and now he's getting to experience it in his own way in full. It's a very meditative and smooth experience for him I think. He's just sort of gliding along the waves. I find this to be completely refreshing. It also maintains the mystery of the future very well.
All of this. All of it!
Fire walk with