So is it basically then that John is not the center of this trinity, but Sam is? Because if Sam and John still butt heads, then the "You're SUPPOSED to take care of your little brother!" would strike harsher. And Sam DOES take care of Dean, god, all he does is take care of Dean it feels like. On hunts, on bar nights, on hustling nights, on 'oh shit the cops are after me' nights, on 'oh shit some woman's husband/boyfriend/brother/dad is after me' nights. Oh Dean, thinking he can get by on fast cars and winning smiles and enough bullets. And Sam starts getting claustrophobic and thinking of escape, maybe, but these uncharitable thoughts, these thoughts aren't fair to Dean. (Here is where 5.16 would differ maybe, because if Sam is an older brother with 'take care of Dean' ingrained in him, then he wouldn't just be seeing Dean as collateral damage of leaving the family. Dean would be so much more than that.) And maybe Dean's a little messier as a younger brother, because maybe he starts taking Sam cleaning up after him for granted.