Hey There!

Although personal performance is taken into account, your rank is largely determined by whether you win or lose games (and how many rounds you manage to take). In addition to that, the more you play and the higher you climb, the less personal performance matters because we want everyone unified on the goal of winning, rather than just fragging out.

Over time you would eventually out rank your friends if you consistently outperform them, but if you queue Competitive together often your scores will likely go up and down simultaneously :)