As far as I know, matchmaking is based on a hidden ELO within the normal games, no matter what level you are. If you're a pretty good player, your ELO will go higher, and you'll face tougher opponents. On average, this means facing higher summoner level opponents, simply because they have more experience with the game so will tend to have a higher ELO.
The thing with arranged teams is that it averages out. Meaning, and this happens a lot with me, I usually play with a friend of mine who has been level 30 for about half a year now. I've started playing a few weeks ago and am only level 15. Needless to say, he is a great player while I'm rather mediocre, so my ELO being low, and his being high, it averages them out to whatever, usually around level 23-27. This might explain why you're facing crazy god-like level 30s at such a low level.
It does suck, and I feel your pain. At least when I play with him, I'm 100% always fighting players who are better than me. However, I think RIOT has prolly the best system in place for the moment, one that's based off player skill instead of player level. Level is is a function of time, not necessarily skill. Skill is a function of, well, just that.