I've had this same thought, but remember we didn't see what Dougie was really like pre-Coop morph. Perhaps that is what Dougie is like - we know he drink, we know he gambles, we know his son finds him funny - is that just normal Dougie?

The guy he meets in the casino does note him as acting oddly, so we can assume something's changed from Dougie to Dale.

No one in the state Dale's in now could have met a woman, helped raise a child, hired a hooker, got and held a job.

Indeed: sad how the security guy in the evening square (end of S3E5) tells him not to loiter at the statue and to run along...

For the brief moment befor being pulled back to Black Lodge we see real Dougie Jones with Jade and he seems to be normal guy. Later Jade ask him if he had stroke because she realizes he acts strange. 

Hot-dog guy in casino who knows Dugie also sees that he is not ok.

I think it's Lynch's satire for people trying to be correct for all cost. He likes to explore disability topic. It is sad how other people react to DougieDale state, pretending everything is normal.

Poor Dale lost in Dougie's life...

Janie-E tells him that he's acting "weird as sh*t" right before they get in the car.  But she doesn't seem alarmed, just annoyed . . . .

Janey-E also talks about Dougie having one of his episodes again, so he might have been a normal dude with some mental troubles triggering occasionally. We also know he likes drinking and gambling and it seems to happen in an unhealthy way like disappearing with hookers and owing 50k to the wrong people.

And Dougie is welcomed back from "Bendersville" (I think) by the colleague who says that he covered for him (and has probably done so in the past), so I think he's had some issues with the bottle in the past. 

Or maybe some of his "episodes" were caused by his connection to the lodge spirits, which he always had, even if he didn't know about it.

Could it be that the colleague supplied Dougie with the key to his house-for-sale in Rancho Rosa, so that he could have 'a ride with Jade' without Janey-E ever knowing about it (Janey E, when laying eyes on MemoryLossCooperlostinDougieJones'life screams 'Where have you been these last three days (!)?'? Before the boardmeeting the liar colleague was acting all boys-will-be-boys with who-he-assumes-to-be-Dougie. The grabbing-him-by-the-shoulders and 'Look who's back from Bendersville?' was translated in Dutch subtitles as 'Have you been out having fun?'

No one has asked who is Dougie?  Apparently he is NOT Cooper, or at least the body seems to be Cooper.  Cooper has not been restored to his body and intelligence.  We presumably know where his "essence" is, (now waiting in the slammer). . .

Do we know for a fact that we are seeing the post black lodge Cooper returned to an obviously not his body?