“Don’t you dare think that there is anything past or present that I would put in front of you"
It's not actually true, that speech of Dean's in Sacrifice. It's a retcon. When they were kids and young adults, Dean was completely torn between John and Sam. He didn’t love Sam more than John, and he didn’t value Sam more than John. After the Stanford fight, he chose to stay with John rather than try to reach out to Sam. I don't think it's a coincidence that Dean in the Pilot shoves himself back into Sam's life after John goes missing. Dean's ideal, of course, would be to have Sam and John get along - but he does not consistently put Sam above John.
This changes in S2. Dean's decision to sell his soul for Sam is rightfully seen as very important - but perhaps equally of import is his choice not to do so for John, in Crossroad Blues. Those two decisions mark an essential change in his relationships with and attitudes towards his father and brother.
This changes in S2. Dean's decision to sell his soul for Sam is rightfully seen as very important - but perhaps equally of import is his choice not to do so for John, in Crossroad Blues. Those two decisions mark an essential change in his relationships with and attitudes towards his father and brother.