I was actually wondering the same thing since this episode aired, Gaelic. I totally agree with you in everything you said.
And even this "twist"... Ok, it might have surprised some fans, but me... I don't know, I didn't think it was THAT drop-jaw, you know....
Because of this comment:
come Friday morning we’ll be talking about an entirely different wrinkle in the Supernatural drama
Maybe this guy had in mind the last scene, Dean telling Sam that he is more alike John than himself. But I don't see any twist on this, either. Since season 1 we kind of know that already and more on season 3, in the episode "Mystery Spot".
And really... It didn't distract us from the fact that Adam was John's son and especially the way John treated Dean and Sam as soldiers while was a lovely father to Adam.
(Yeah, I'm still mad)