See? That is the problem here. You had a bad matchmaking in your favor to begin with (which should never happen according to you) and your enemies had to lose because of their bad mates. In an upper post you said "as long as you don't troll yourself, your chances are higher". According to that, nobody trolled intentional, yet had to lose and then ragequitted.
You are prolly saying you were fine and the enemy not. Now imagine the OP is on the enemy sides that were crushed and had the leavers. OP is not overly toxic, and maybe fix his built, but still loses like that. Is his opinoin and experience now invalid?
In other words: You just showed how flawed your logic is. Player X and Z of your opposing teams might have left because of a "lost game", yet they lost and left. Player W, Y and V however were dragged down by this leaver, and they might be the friendliest guys on earth. Now what? Explain how this matches your reasoning?
As said, probability is one side of the coin, the other one is to use that cheap reasoning all over when people say they have a leaver streak. I am here since 2010 and this is getting old.