This was my problem with the Michael arc. It wasn't about Dean. Jensen played Michael but the story really didnt' involve Dean much.
The first ep we didn't even see Dean. It was a 3 short scenes shoe horned into the ep with no direction. Even Jensen didnt' know which way to turn with the character. Ep 2, I will admit was better, but again we saw Dean for literally 10 seconds. (if that). It did set up something interesting stuff, but it was dropped for now reason. Then Berens threw out the story by making it about Kaia. Michael was taken out handly by Ninja Sue.
Then we had no follow up. The Scar branded Dean as the bad guy with one half hearted line of defense. Dean says he's too weak to defeat Michael in which the camera directly focuses on Sam while he's saying.
Episode 4 Dean seemed more upset about the AU people.
The we had Michael's so called plan to drive Dean crazy that lasted about 30 seconds, and was dropped after that for sick dying Jack ep.
The main scene in ep 9 the was given to a guest star and Jensen got two minutes of screen time. The Nilishm, which Sam was the one that actually locked Michael up.
Dean was branded as weak and quitting when he wanted to sacrifice himself, then Michael got out and possessed Rowena for the Jack confrontation. The in the follow up ep, Dean was literally not mentioned. Rowena got more follow up than Dean.
If Michael lead to bad things happening to Dean, bring it. anything would have been better than Dean being sidelined in his own story.