Doesn't matter. Stop bringing it up. The general trend doesn't exclude other possibilities.
The "general trend" has born out the only definition of demons we have been given. It doesn't exclude deviations, but neither have there been any deviations to be excluded.
Yes there is. It means that he's capable of revenge. Revenge implies capacity for feelings, not just imitation of them.
Who says demons don't have feeling? I never did. Demons, however, restrict themselves to a very narrow range concerning the idea they have chosen to embody. Their goals and desires are entirely focused on fulfilling those ideas. Let me be more clear, he killed the clan because they chose to imprison him and Michel chose to free him. He was simply creating the consequence of choice. I don't recall him attaching any particular malice or anger to his actions.
You don't know what his goal is. Killing Fellesan doesn't fit your theory of mayhem. It doesn't result in that. It's because of something else.
We don't know what killed Felassan. I find it unlikely that it was Imshael. He seemed quite surprised when Felassan intimated the coming chaos, certainly not like he was involved in the plan. Personally I think it was a Dreamer. (An aside, that ancient elf idea of mine may not require bodily resurrection. We know mortal spirits can become stuck in the Fade after their body dies, see Niall in Origins. An Ancient Dreamer might be manipulating events from within the Fade) Until we can say otherwise, the incident is irrelevant.
You're still saying that like it's gospel, but it's not. It was stated multiple times by developer, that the lore we know is not the lore that is. Here's my proposition. If a demon embodied more than one emotion, then it would be complex, and as someone who just read the Masked Empire, I can tell you with confidence that Imshael is complex. It is heavily implied throughout the book. But guessing that this won't change your mind to admit the possibility of complex demons existing, let's agree to disagree and we'll see who was right when the game releases.
Imshael is not complex, the idea he ascribes to himself can be. You're mixing the two up. All Felassan had to do was dangle the possibility of future chaos in front of him and Imshael was happy to go along his merry way. Knowing there's more to the lore than we know isn't the same as assuming the lore we know is wrong. I'm going off the information we have, not speculation.