How to make the ranking system fair.
You have no control over the other four people on your team, so why is your ranking based solely on whether you win or lose? Here's a better idea. Kill = 2 points Assist = 1 point Death = -1 point (maybe this should be -2?) Win/Loss = (+/-)5 points I couldn't decide whether deaths should be a loss of one or two points, because Tank deaths can be beneficial, and same with Support. (i.e. Dying to save teammates.)
So let's say you go 7/2/5, and your team wins. You'd get 22 LP. Same with your team losing, you'd get 12 LP.
If you had gone 2/7/5, with a win, you'd gain 7 LP. Same with a loss, you'd get -3 LP.
Another idea, instead of gain/lose points for win/loss, it could be that deaths are penalized harder if your team loses.
The point is, there should be more to your rank than whether you win or lose. P.S. Something like this could solve the problem of getting carried to a higher rank.