Broken Matchmaking system (and vayne rant)

So recently I've been playing a lot of ranked trying to get myself into gold, and one thing I've noticed is the team I've been getting right after I lost my 9 win streak progressively got worse. What I've also noticed is the fact that the enemy teams keep coming back from really far behind, this has happened 3 or 4 times in the matter of about 5 days. Champions that are complete BS in low elo (Vayne, Nasus, Master Yi, Katarina, Yasuo) have a really easy time carrying games. I'm especially looking at Vayne, she is so dumb as an overall champion. "PASSIVE: Vayne's basic attacks and abilities mark her target with Silver Bolts for 3 seconds, stacking up to 3 times. The third stack consumes all Silver Bolts on the target to deal them true damage." That is the most ridiculous sentence I've ever heard. It's really easy to learn how to play Vayne and there isn't a lot to be done to counter her, she has self peel, ridiculous damage, and her chase is stupid with her passive. At least make her w cost mana with every basic attack (kind of like Ashe's old 'Q'). Well that's my little rant, down vote or whatever, doesn't make a difference to me. Just thought I'd get my feelings out there.