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.
You have to play meta characters
No, you do not.
Meta means nothing up to Celestial level. There were plenty of proofs that even above the Celestial you can play whatever hero you like. E.g. Mister Fantastic mainer who got Rank 1 playing only that character when everyone said he is F-tier.
We’re talking about Celestial+ as an exception here, because on that level the game is more built around counter-picking and team play than individual performance. But you can carry a game if you’re good enough even when being hard countered.
Most of the players are not in the Celestial ranks every season. We all played in Gold and Platinum where the game can be literally be carried by Rocket Raccoon playing damage only; or a very talanted Squirrel Girl which somehow nobody can counter. So, stop being a meta slave and just play the game you like.