Bronze? 0.o;

So I've been from Bronze 1 to Bronze 5 and back again, and I'm not quite understanding why it is that I get paired in games with people in a lower bracket? Shouldn't Bronze 4's be competing against other Bronze 4's, etc.? A few games back I went against a team (I'm B4) that had 3 people who were Bronze 1. They obviously ripped my team's butt, and none of us had anyone better than Bronze 3, with two being Bronze 5. What's fair about that? --- I'm not quite sure how this matchmaking system works in this instance. I thought these brackets existed for a reason? Why does the matchmaking system basically have a "Bronze mix?" I obviously play at a Bronze skill level, but there's still supposed to be some skill difference between the brackets, I thought? A B1 should be better than a B5, right? So why is it pairing B4 & B5 players against B1 players?

I think it's a little absurd to expect a B4 with a team full of B5s to carry a game by himself against a team of 3 B1s and 2 B2s.