Ranked MMR

Does the system place you against stronger enemies and/or with weaker teammates if you try to main a champion? I could play better yes, but I'm almost never feeding and still losing a large portion of my last 50 games.

I'm not pissing my team off. I do help them or my scores would be something like 2-0-1 which they usually aren't. I should do this more but I will tell them not to fight outnumbered if I catch them doing it. It works about 20% of the time the other 80 they don't listen at all. Is it back luck? I'm not sure how this measures statistically.