Is this what you mean?
Wyll at one point (as well as Gale, I think), recalls having been extremely powerful, but now being reduced in power since the tadpole. Laezel also speaks of tremendous feats of power (though, she could well just be bragging/exaggerating/lying). And Shadowheart has these flare ups, as well, that she doesn't recognize. It does appear as though something has been 'lost,' so to speak, in this transition.
The most perplexing would be Astarion's... well, changes, no longer being subject to the rules that he 'used' to have to live by. It does appear that there is a sharp disjunction between who we were before the tadpole's insertion and now.
To go along with your argument, perhaps Astarion's belief about his 'former' self, for instance, is just that: entirely constructed. After all, we all came out of the mindflayer pods, and we remember how quickly someone can "transition" in one of those pods: at a flip of the switch, apparently... It was portrayed to us players as a "transition" into a mindflayer: perhaps it wasn't a transition at all.

Last edited by RadiantHeart; 24/07/21 08:31 PM.