I don't care much for the inconsistencies Sceleritas may have brought with his comment, but I do think the evil endings are clearly phoned in and written without any interest in them, just trying to get them out of the way.
I want to add that it's not even just comments that Sceleritas made, but also dialogues you share with your romantic partner as Chosen Dark Urge, and the prophecy made by the Bhaal priestess if you're romancing AA
If Dark Urge comments that their partner holds the key to immortality, the Bhaal priestess gives the prophecy of AA and Dark Urge dying in each other's arms, at the end of days, when the sun explodes. Apparently that's not even an option now. The only options are to just kill your partner immediately or make them run from you for now, basically with the promise of hunting them down to kill them later.
I believe that can happen regardless of if you're the DU or not, as long as you become the Unholy Assassin. And then, even as the DU (if you don't embrace Bhaal) you could also just choose /not/ to conquer the brain, thus having the prophecy be possible.
EDIT: My bad, while you do need to become the assassin, her question is locked behind the flag that you're the DU. But you could still choose not to embrace Bhaal afterwards, I think? I believe the choice to become the assassin predates the encounter with Orin, but it's been a hot minute since I played full blown evil durge. Also, to be fair, you can already as the player take steps to break her prophecy after the fact, if you wanted to (of course it feels a bit different for the player if they chose it or the game chose it for them) by, for example, becoming a squid. It's not set in stone. Alaundo also predicted Aylin's revenge, but that can also not happen at all if you so choose.
Well, all that's to say: I don't find such inconsistencies all that important when there's a bigger, glaring issue with these endings, in my opinion. A lot of this stuff you can handwave away pretty easily "Sceleritas was lying" "Her prophecy was just poetry" etc etc. It doesn't seem the craziest thing to me that a Chosen of Bhaal wouldn't want to create more life (as Sceleritas so... succintly describes) rather than ending it for everyone.
