I think the problem with Viconia's depiction, more than anything, is it simply seems, like...lazy and uninformed.
Like it's not a problem that she's evil, with no trace of her possible redemptive path. It's just that even "evil" Viconia in BG1 and BG2 was a more nuanced evil. Even if you KEPT her evil, she was still an evil that had felt an intense disgust over what Lolth had demanded of her.
And like, the thing is....you could have had her do almost exactly what she did in BG3, and still be a good character, a commentary on the nature of evil. Shar is still evil, after all, she is the lady of loss. Maybe in the end, what Viconia lost in her years of service to Shar was herself. Like yeah, she is now doing things that bear somewhat of a resemblance to what initially disgusted her about Lolth, and that's the point. She's not "Viconia on the redemption path", she's evil Viconia, and after all these years Shar managed to do what Drow society and Lolth could not: Extinguish the one little spark of conscience in her.
Viconia could, with a little more writing and backstory, do exactly what she currently does in BG3 and come across much better. She would be a tragic figure, and maybe some fans of the old games would be sad that she couldn't be more like the Viconia they knew in BG1 and BG2. But she could be a commentary on the nature of evil, and a striking demonstration, especially for fans of the old games, that evil is what Shar *is*. The danger that Shadowheart faced is written in Viconia here: The Drow that once rebelled against the insane demands of her evil god now reduced to this, made less, by the years of her service to Shar.
Maybe I ought to give Larian the benefit of the doubt, maybe that's what they were going for. But it didn't really seem to come across, to me. It just sort of came across as "Wow look! Fun cameo by the EVIL party member from the previous games!"
