So here's the paradox in the series finale:
On the one hand, we have been told for years that Dean has no self, that he needs to get a life
other than Sam, that he and his love are overbearing, that he needs his own core and can't
just glom onto Sam, that he has no self esteem or self respect, that this is all wrong,
yada, yada, yawn.
Sam even wants him to go out and live a normal life after his sacrifice, so Dean can finally have
a sense of self, live for himself, not for and through Sam.
And then it turns out that this overbearing, selfless love is what arrests Lucifer in mid kill,
that allows Sam to re-emerge from lurkdom and strengthen him enough to overcome Lucifer
and jump into the hole. In particular, Samifer lingers on the image of Dean hugging him
after he sacrifices himself with one year to live and Sam returns to life, and that's the thing
that causes the change that accelerates into full on control by Sam.
So this very quality of Dean which is so often ridiculed and is brought up again and again
to give Dean incentive to move beyond it is the very thing that Sam needs to connect to
in order to play the role he wants to and end the apocalypse, as opposed to jump starting
it into further havoc by remaining Lucifer.