I'm gonna confess something here: I remember being more invested in dylan's implied marriage problems that were only brought up in one scene than I was in the rest of the plot of s15. fuck the blues and reds, fuck dumb grimmons drama, fuck locus redemption, I want to know if dylan's going to get divorced!
Doc and O'Malley are my favorite guys ever. They hate each other, they depend on each other, they want the other gone, they taught the other so much about themselves, they want to beat up each other personally, they bicker like an old married couple, they're enemies, they're partners, he's tortured for real, he's a cartoon villain, they're nothing alike, they're the same guy
While I sympathize with being frustrated that your favorite character wasn't the center of a story, I must point out that he had three fucking seasons where his character arc was at the core of the show, that was probably the best of it, and maybe it's fine somebody else got one that wasn't even particularly good.