Sometimes it's not a mechanical difficulty, it's a matter of playing into your natural temperament.

I'm greedy, impulsive, and irresponsible and play really aggressively and am way too competitive. I do really well with Reaper better because he rewards it. Yes I am ashamed.

My partner is non-confrontational, conservative and has great self-discipline and crisis management skills, and does really well with Mercy because she rewards it. She bails me out of the consequences of my decisions and likes to babysit the team from behind a wall.

Our temperaments compliment one another well and we can perform well in much higher levels of play when we group together.

When he's not around and I'm playing with strangers, I have no problem playing support if that's what the team needs and no one else will step up to bat. I'm just going to suck at it and our team is probably going to lose.

Aces in their places, dude. Unfortunately most Overwatch players are self-obsessed and impulsive and mistrusting of others, and will therefore play DPS exclusively.