Is a goddess's evil all that there is to her? We would say "no" about almost any human, and Toril's deities are actually ascended mortals.
So, Shadowheart might not be brainwashed, but right. From her perspective, following Shar may appear right in a way we would recognize as valid could we adopt her perspective. With no need for any evil on her part.
Many are ascended mortals -- AO has reasons for wanting mortals in certain positions and he changed the tablets of fate to ensure that Deities answer to their worshipers BUT Shar and Selune aren't ascended mortals. They were born as gods. They were the first two and haven't changed that much since their initial battle:
In order of appearance:
1) Shar 2) Selune 3) Chauntea
Chauntea has changed over years from a goddess of the wild places to a goddess of gardens and cultivation but is still born as a god and thinks like like a god. Of all the gods Shar has probably changed the least over the millenniums.
I think Jergal was also originally a god rather than an ascended mortal. And even though he decided to give up all of his positions of power out of boredom I don't believe he's mortal or a lesser deity either. He was the original god of death back when the responsibilities of the god of death encompassed all aspects of death unlike now when we have at least half a dozen gods messing with various aspects of death...Bhall deals with murder, Myrkul dabbles in necromancy and undeath right now, the Raven Queen oversees that the cycle of life and death isn't cheated and sending agents to take down liches and others who would seek to cheat death, and then there's some other dude who oversees the judgement of souls who are not claimed by any other god after death.
But Jergal is ancient, powerful, and still around...I very much suspect he'll make an appearance in BG3 now that the three he gave his office powers to have reunited and are up to trouble. Swen saying that the player character can become ruler of the forgotten realms in BG3 suggests that at least the power of the three if not some more as well might be reunited into one again. If the player is evil(at least for the Dark Urge) he can claim that power for himself...but if not then what? My guess is Jergal could be a candidate for obtaining some of his old powers back from the dead three as a more neutral holder of power should the player not take it. But if nothing else he created the dead three by giving them his powers, it is only fitting he is there at the end of the dead three as well.
