Matchmaking Balance

Why do I have to 1v5 to climb?

My brother gets carried frequently in Plat, but I'm stuck in Silver with a much higher kda, RARELY get carried, and quite frequently have to 1v9. I know I'm better than my brother because I see him make a lot of mistakes that I don't make usually and he has next to 0 Macro knowledge

I've reduced the amount I play ranked because of how insufferable it is, and I'm close to giving up this game entirely.

Riot dev team please reach out this is not a shit post more a plea for help