I've just finished running one of my power-based avatars through episodes 8 thru 10, and as I expected my power-based build made it through everything much, much more easily.
All of this started when I got bit by the bug that stalls a character in episode 8, scanning the Tier 2 rifts. Arenanet has tickets on this issue (see the thread on this forum about it).
My favorite power build was the one that stalled.
So I switched to my condi reaper and worked the story with it. I hit episode 8 and didn't get hit by the bug. However, the problems I described are/were real.
My condi reaper has full ascended gear and all sorts of CC and Defiance Break capabilities. Apparently, however, I needed more burst damage capability, because I could only get half-way to killing that green-X essence before it rejuvenates the possessed Isgarren avatar
Your comment about DPS resonated with me. So I bought an uncommon Kryptis Motivation for 3.8G that's the current workaround to deal with the stall bug, so I could run my power build (a scrapper) past the stall to finish the story. My scrapper had no problem with Isgarren . . . in any of his forms
Anyway, thanks for your thought on this; they helped
I'm wondering if others with condi builds have experienced what I did with mine. If so Arenanet may need to address a power build "bias" for that particular boss