So while reading other threads here, I had a realization, one I think could relate to why Daisy was replaced with the guardian as a character archetype. This is specifically about the change from Daisy to Guardian, not about the Emperor.

So in EA we heard that each companion saw a unique person tempting them. We all said how cool that was and what replay value it could offer for playing as the origins. But it's only now occured to me... how could that temptation actually work believably? Daisy was impersonating people who the various companions specifically knew they couldn't be. Typically impersonation only works if you could actually be the person you're impersonating. However in Wyll's case Daisy was supposedly posing as Mizora, but he's still ACTIVELY talking to her at that point and he knows she's been abducted. Daisy also took the form of Cazador for Astarion, probably the person Astarion hates the most. How's that supposed to tempt him? And for our character it took a generic form we created that offered us generic power and destruction. Not only that, but the party all knows they have a psionic parasite in their heads, one that easily has the ability to make them see images, so they would be even more on their guard. Presenting as the same person for everyone, as an unknown factor claiming to have a common enemy may not be inherently trustworthy, but it's at least got fewer red flags.