You’re 10% of the match, but you can have much more weight on the end result of the game than just 10% (no need to be a player like Fan who probably affects 80% of the end result when playing in low leagues).
You can make game deciding plays and plays that the enemy can’t recover from (like chunking down 70% of their core alone) even if you are just one player out of ten.
Then your win rate slowly climbs over 50% and you start ranking up.
Needless to say, and it has been said plenty above, this is much easier to do in a party with trusted skilled friends.
The chaos factor when playing with randoms is huge. AZJackson himself went on a 16 loss streak at the start of a season, and he was a senior game designer whose skill level in-game is high Grand Master.