No sense with this ranked

I want to report some issues, with matchmaking can you explain to me how is it possible that I play 4 hours a day, average 30 assists, 20 kills from a healer, hello the whole team, we go into overtime I keep healing, and in the end, I lose??? Because this game has no meritocracy, I’m stuck at gold 3 but the matches find me with a diamond rank
Explain???