I agree with 99% of this. But to me, it was important that the AU hunter was _not_ John. Because the divergence point was not Dean’s birth. It was earlier. In that universe, Mary did not make a deal with Azazel for John’s life.
Which means that Dean has forgiven her for making the deal in 12×22, and then he gets to see what happened if she didn’t make it. (And it was so important it happened in that order.)