I wouldn't mind if blind pick was balanced, but it isn't.
Let's say everyone starts at 0 MMR and for each victory you gain 50 and each loss, you lose 50.
So I started a new account, stomped some complete newbies for first 3 games (or got stomped because I had newbies on my team and enemies had "smurfs"). But for current sake, let's say I won. I'm at 150 MMR and system detected that I'm not a new player, so assigns me with similar people. Since I play better than average folk there, I win more games in row (let's say 5) and my MMR spikes to 400. Now average player's MMR at that point is lower, but since I'm above average skill level mine is higher. But Riot doesn't like much higher than 50% win ratio, so match making decides to match people with lower than average MMR with me and people with average - slightly above average MMR to enemy team, with hopes of either me losing MMR or my teammates gaining MMR.
But since teams are something like this:
Allied:
0 MMR
100 MMR
400 MMR
200 MMR
50 MMR
Foe:
200 MMR
250 MMR
100 MMR
100 MMR
200 MMR
It means that enemies will most likely win.
Problem is that match making puts teams together by looking at what is team's average MMR, but it should look at player's individual MMR.
So teams should be:
Allied:
300 MMR
400 MMR
450 MMR
200 MMR
250 MMR
foe:
250 MMR
300 MMR
400 MMR
500 MMR
200 MMR
Teams are practically balanced. Every one has similar MMR and match will be more fair, not a stomp fest for one side.