Lowest rank I've ever been is 2623 and I'm currently 4200.
Aim aside, I believe awarness and positioning makes a big difference. But communication really did help a lot. Ability and Ultimate management is extremely important as well.
and hero pool, well, I personally like to Flex to any position. Depends on the player tho.
My best tip to improve is to record your gameplay and watch each games. Stop playing the way you normally do.
If you're in platinum playing like a platinum, you'll stay in platinum. You gotta be better than a platinum to climb.
Watch where you died, when you used your ultimate, was it a waste?
The enemy genji had has abilities on Cooldown, did you punish him for it?
There's a lot of things you can focus on improving and it will def help you climb