I don't know why but I'm seeing the same thing happening. I usually have a pretty decent winrate, but playing an alt the past week or so has given me an unusually high number of incompetent groups. I lose almost every game. Obviously one could argue that the gear difference between upgraded arena gear and contender's is pretty enormous, but I really doubt every bg on my main is only won because of my gear. It just feels like I get grouped with less observant/intelligent players when I'm on an undergeared character. There's got to be something more complex to bg queues than just luck.