Of course we're getting less. Again. It's the pattern established by HW, SB, and now SB2.

I'd wager trusts are to blame. Coding the NPC's to be able to react to mechanics probably takes up a chunk of development time, to say nothing of what is already spent on environment design, music and enemy models.
We've been getting a steady decrease in the rate of dungeons per patch with every expansion, before the trust system even existed. I assure you that this would have continued to be true even without the trust system.