I agree that Dean's a lot more than he thinks he is right now--I see him as, in some ways, very realistically depressed, narrow-focused in the way depression can manifest. And you explained exactly why--he tried his best, agreed to give up the thing that defined him for good or ill since he was four and his/Sam's sacrifice just led to horrible torture for Sam and the release of some bigger bads.

Dean's always fit well into structured situations (prison, the film set, construction work), so I think if he regains his understanding that the supernatural isn't always and irredeemably evil he could rebuild the institutions that have been destroyed--the Roadhouse, Bobby's house--and (in my perfect ending) train people to hunt what needs hunting and to remind what might need hunting that there is a sheriff out there.

I would love it even more if they did this with Dean and Sam building each other up; I think it's still possible.