Not trying to be rude, just quoting because these are classic "bronze" misconceptions. (Actually effects most tiers except maybe top 1%.)
I'm very close to bronze. Statwise my mercy has similar stats to people in grandmaster. I have decent aim but slow reactions (old).
Don't look at grandmasters, it's not comparable at all. You can "accidentally" get the same stats as Grandmasters simply because opponents are knuckleheads. In GM your opponents are actually good, the effort to achieve the same stats in GM as someone in Bronze/Silver/Gold.../Plat is exponential. It's much harder to have good stats in GM. Your stats should blow away GM stats.
My biggest problems are that I don't join voice.
Voice isn't that big of an impact. Mute everyone every game and you're likely to progress much faster than if you don't. Voice is a distraction and a tilt-machine most of the time. Voice only relevant in pre-mades/top tiers* and the rare occurrence in solos... but usually only because your team is already winning. (even in top tiers it's probably very toxic, but the playerbase is more capable of dealing with it.. more tilt-proof).
... and I seem to consistently get terrible teammates.
Terrible teammates should never be an excuse. Yes, there are terrible teammates and unwinnable games, but being "stuck" in an MMR is normally a result of your own play. (Being stuck means unable to progress after many games). If you're at or below a 50% win rate, then that's on you.
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I bounce between Low-High plat and that's my zone. I play DPS 99% of the time and if I really want to break through, I probably gotta pull a Tenks and learn Support/Tank.
But I don't want to.
And sometimes my DPS play just isn't sharp.
And a lot of times I don't realize I'm in a funk until after my 5th loss in a row, and I reflect on the games. Then I realize I'm stressed/tilted or just tired as hell.
And then I keep playing "just wanting 1 win". And 3 losses later I get one of those "unloseable" games... And I'm content.
Then I sleep, and the next day I'm on fire and go on a 10 win streak.
And the cycle continues.
One day I'll lose a few and quit. Then go in the next day and actually get ahead.
And sometimes it happens and I reach 2800-2900 and think I can get that 3k.
But it's a trap, and I lose focus, and then fall back to 2600-2700.
Etc etc etc.
The life of competitive gaming.