I agree that matchmaking, at times, is like WTF??
But I don't think it's an easy problem to solve, if it's even possible.
An entire team of 2 k/d + guys will destroy just about anyone in the game. The only way they could be beaten would be by another team of equal skill. And teams like that are crazy rare. How many full teams of players of that skill level do you think are playing any given mode at the same time? Not many. They are probably the only one, or maybe there are one or two more. Should those parties have to play only each other, because that's the only balance that is possible? Or do you just say "sorry, you guys are too good, you can't party up right now."
The game does seem to try to match up parties with parties, but does not have as much concern for size of the party, it seems. Probably because if it tried to match 6 man parties only with 6 man parties, it would take forever to find matches because there are not enough 6 man parties playing the same mode at the same time. But if you are playing with 6 people, it doesn't seem to drop many singles in against you, it's usually parties of 2 or 3 or so.
It's happened the other way around to me too, though. I've played by myself and gone against crappy "clans" or parties TONS of times. Countless times. Most times. WAYYYYYYYY more often than going against a good party. The balance system gets screwed by this as well, if a bunch of friends party up, who are not very good, they will continue to lose because the game can't add anyone good to their team to help them, or anyone crappy enough to the opposition to let them win some.
It goes both ways, and IMO, much more often the party sucks than is amazing. This is why I swear by playing against parties. I love playing parties because 99 times out of 100 the party is actually making it harder on themselves by not allowing the balance system to do a good job. I'll disclaimer right here -- this is NOT true for objective modes!!! TDM only...
The problem is that the balance system has trouble doing balancing when you throw a monkey wrench in there by being in a party and basically saying "we don't care about balance anymore, it is more important that these exact people are on our team."
I do think there is room for improvement with respect to matchmaking -- it's far from perfect -- but if you think that there will ever be balance for a team full of the best players in the game, you're dreaming
It's more likely that the balance could be improved if you are part of a crappy party, because crappy players are in greater supply.
And FWIW, all of my comments are directed at core mode, and only about TDM. Objective modes are a whole different ball of wax.