first in matchmaking lobby hit x And pick close skill range That should help.
another thing, in the play list you play A lot, look at your experience in that play list. for example, I'm a captain grade 3 (look at my bungie.net profile for proof, search Spartan 1522) I've rarely played team slayer or social slayer since the new exp. progression system update. therefore my experience is very low in that playlist but I have a pretty good highest skill. So I end up in games with everything lower than me, so no offence to your rank, but I own all of them, usually have around 20 something kills when 2nd on my team has like 9 or 10.
So next time look at their play list exp. If it is close to yours that's why. But always focus on highest skill, that gives you a better idea on how good they are