Kills means everything
There are two myths in one.
First, vanguards and strategists always never have the same amount of kills as duelists. If your Luna Snow has more kills than your duelists, it means either Luna does not heal, or duelists does not kill. Rocket Raccoon usually never has more than 10 kills, and it’s okay. The amount of kills is not a universal ruler.
Second, for most heroes kills mean nothing. Finals hits do. You earn a kill point when you damaged a hero and someone else killed him. On the other hand, final hits are earned when you actually eliminate an enemy. With this system you may have Moon Knight with 30 kills and 3 final blows, and Spider-Man with 10 kills and 9 finals. The Spidey is doing much better than MK, because the last one is just feeding damage to enemy supports.
Damage means everything
Same as for Kills means everything. If a duelist have a lot of damage but does not have finals, they just speed up enemy supports ultimate’s charge.
The higher on the rank ladder you climb, the most important is to have clean eliminations with no excessive damage. On Diamond+ you’re playing resource-based strategy, not just a shooter.