It is hard for me to think about this because there are different layers that I have trouble keeping separated.
One layer is what Dean felt about his fate. I think that because he had been hunting and putting his life at risk on a daily basis almost his entire life, he had always expected that this would be his end, and although he didn't want to die, he accepted that his time had come. Which is not the same thing as wanting it to happen; he did not want this to be "the day".
For me this is separate from whether or not Dean felt he deserved to die like this. He was definitely damaged by the life he had led and the things that had happened to him, but I also think that we had seen him reject the idea that he was nothing more than a blunt instrument or a killer. Although I agree that he still really could have used some intensive therapy for his issues, I think he believed it when he ultimately told Chuck, "That's not who I am."
On another layer is what the episode was saying. I don't know that the episode was necessarily saying that this was the bestest happiest ending ever for Dean; it was acknowledged that this was a sad thing. But Dabb, in the way that the episode was written, completely ignored how horribly and monstrously unfair and awful what happened to Dean was. (I feel like I need a stronger word than unfair.) And the episode did seem to be saying yes, this is sad, but hey, it is kind of lovely and poetic, isn't it?
And then there is one more layer, which is the viewers. And I do think that there is a subset of fans (not anyone here) who absolutely are saying "isn`t that the bestest happy ending ever for him, yay". Not necessarily because they think Dean is better off dead or he is too broken to live, but because of what Aeryn and Tessa mentioned, the romanticizing of the idea that it is so beautiful to see Dean die and go to Heaven and wait there for his brother to come join him, because that is Dean's perfect destiny.