I also have a feeling it's instance related. I'll quote what a very intelligent anf attractive player just posted a few minutes ago in another thread before seeing this one:

Something I've wondered.... is part of the slowness due not to the lack of being matched up with enough people across all GC's, but due to the availability of enough Instances. What I've noticed queuing for dungeons is it will fill up the party- tank/healer/DPS at 1/1,1/1,2/2- and say Waiting for Instance for quite a bit longer than I'm used to. And I can't help but think the reason is because of all the bots standing around the Uldah Aethyrte I see queued up popping in and out of instance constantly. So in addition to bots causing QoL issues in so many other regards (RMT and running an uninterrupted spiritbond farm using the same characters in North Shroud for over a year now) they're taking up our instances. I don't know if PVP shares server capacity for instances with dungeons, but if it does that's part of the problem.

One way or another, I don't think there seems to be enough instance capacity. You can't tell me that in the evenings it takes over half an hour to find enough people across all GC's, across all worlds in a data center, to kick off even an 8/8/8 instance.