As I see it, the show has been mostly about Dean for most of its run. Dean's feelings, the way Dean handles things. Dean's been the heart of the show, even when the plots were about Sam. And don't get me wrong, I adore Dean (not choosing a favorite, nope), but that really hurt the show, IMO. Sam got very little characterization, very little agency, even. Dean's the one who saves Sam, Dean's the one who kills the big bads, dean's the one who worries, who comes up with ideas, the one minor characters talk to etc. It's so often all about Dean. The show has been cruel to Sam. But again, YMMV.