I've got the same problem when I play alone due to my kd/r - I constantly get stuck with the 0.50 and 0.65 folks. I've pretty much stopped playing alone and have to beg my friends to play, which doesn't always work as they absolutely despise this game due to the lag and spawn issues.
I've basically resigned my fate to being put on horrible, imbalanced teams. Now, I mostly just try to maintain or increase my lifetime k/d and that usually works out well, even if my team gets spanked by 30+ points. I guess I don't mind going 25-5, even if my teammates prove to be more problem than solution.
Haven't had a ton of issues with lag so far, but granted, my network/NAT settings were jacking up for the past month. Kept getting random Xbox Live disconnects, conveniently during matches where I was doing awesome. But, reset all my router crap and now the issue seems fixed.
Have noticed, though, and not sure if it's a trend, but a lot of folks just running around using pistols and nothing else. And, had a match recently against a guy who was using a pretty effective riot shield strategy of move, plant shield, run around and knife everyone.
And lastly, one more complaint. Noticed that in the past, when someone would destroy my bouncing betty/shock charge/etc, I'd get a VO saying "the enemy has destroyed your equipment," which was handy for me prepping for a possible attack. The past few days, though, I've noticed that the VO almost never plays anymore, even when the equipment gets destroyed. Super annoying.