I can't confirm a damage reduction for my characters. But with one of the recent updates, the AI accuracy buff was increased a bit (and maybe the player's one was reduced by some 5%). Magus Lilith extra turns were a very good hint for that.
I also think there is something true with yup's theory, as sometimes fights against the same players and characters turn out differently regarding difficulty and proc rates.
@huck: the raven lady is in all souls of the right type. I would think that mythics have the best drop chance given the relatively small character pool for assassin!
Also when I looked through your team's I noticed that many wear non-maxed Talis and often of the wrong damage type. Your NotB Ed (I want him too bad!!) only has yellow and purple Talis, these don't help very much to survive if you don't bring a blocker! The very last SQ is hard and as far as I have seen it is not possible to win it without giving the AI some turns on auto play, so your builds must be able to take some damage!
Cheers