I agree 55%?
You're right that it is a change in the lore but I'm okay with it. Largely because mind flayers were / are one of my least favorite parts of DnD lore . . .
It's a change because mind flayers have a god and an alignment and therefore have souls. But, again, no one really cared about Ilsensine and they never played an important role in any major FR event . . . If anything mind flayers make more sense without a god.
On things being living without souls - Tolkein also played around with this with Orc. Borrowing from Aquinas Tolkein had a distinction between fëa and hröa - soul and body. Orcs only had hröa being able to move, eat etc but no immoral force that survives the body.
The story of
Ansur was one of the few bits of the Emperor's story I like - it really shows ceremorphosis for the terrible fate it is. I agree, if your soul dies when you transform than what remains is a pod person / a facsimile / a hollow husk with the memories of the previous host. Ansur was a good friend in denial - he was hoping against hope for a cure. (and a wish spell or divine intervention would have worked).
If you do transform the right thing to do is kill the brain before your mind flayer nature asserts itself and then kill yourself. But, ya know, if you do that Jergal should save the hero by ensuring that their soul makes it to the afterlife.
