I’ve heard it said that the higher ranked person in a duo will gain less win winning and lose more when losing. Over may games, this will cause the duo to have about the same SR. Blizzard hasn’t confirmed this, nor have I seen any solid data. Did you and your friend happen to write down your gains after every game? If yes, could you share it with me (google sheets is best, but in the forums can work too)?
Win streak bonuses are gone. Have been for many seasons. Teamwork can’t be quantified and is not taken into account. Gold medals don’t matter. Statistical performance is compared to other players of the same hero/map in different matches, not your teammates. And that only exists in plat and below. I have a longer explainer at How Competitive Skill Rating Works (Season 10).