I so love that Supernatural has so many layers - or is such a hot mess of badly-written contradictions, YMMV and I don't want to read the hate, thanks - that even that apparently very definitive series ending can be taken more than one way.
Sam and Dean think they won, that Jack won. They relax and behave as if they won, as if all is well now there's an Almighty with perspective and compassion, like they have free will, but ultimately they're plunged back into personal plot tragedy with barely time to draw breath first.
Did they win, or did they end up playing out the finale that Chuck wrote for them earlier in the season - so completely that, like fangirl Becky beta-reading Chuck's crabby, masturbatory, first-draft spooge of his sadistic ending on her laptop after she'd moved on from Chuck's canon to her own AUs, much of the fandom found it appalling, insulting, and unsatisfying?
Not saying they orchestrated a global pandemic to sabotage their own finale or anything, but, you know. Chuck might've. Supernatural 2: The Revenge of Chuck?
*side-eyes reality*
Supernatural used meta as a battering ram to do absolutely unholy things to the fourth wall, and I love to death that it's left me with headroom for both interpretations. And a slightly broken meta-brain.