I ran into this problem with a few PUGs myself. This is the post that Fathom made toward my thread with the same issues. The glyph of DnD really shouldn't be necessary. My rotation differs from yours in one aspect - after the DnD, IT, and PS, I go for Bloodboil first over pestilence. Personal experience leads better results with that.
Overall, just remember that despite the groups and DPS YOU set the pace. If you have to drill that into the DPS's head by letting them take aggro and suffer the consequences, do it.
Sort of unrelated if it's working for you, but why no points in Improved Icy Touch?