I really don't think Larian is trying to actively teach any moral lessons with the game. They have their own perspectives that are appearing in the story, but that happens with every story. But I do find it baffling why they turned that druid immortality thing into a ritual when it's meant to be just an automatic thing that happens. However in defense of Karlach not asking for the ritual to be done to her, the way it works is that druids are ageless, but they can still be killed. So it wouldn't fix the engine. And doesn't Jaheira say that it's a thing for old druids anyway? I've only seen the scene once so I don't remember it very well.
Pretty sure 'evil is supposed to be evil and unrewarding' line from the interview begs to differ pretty hard. Offering perspectives is 'what is evil or good,' eg game assumes x character in the story is justified in their actions or not but the player might disagree personally. BG3 takes it further in punish/reward the
player in gameplay for being 'right' or 'wrong' and often pre-supposes
why an option was chosen instead of letting the player define it. It's what puts far more linear RPGs like Witcher 3 over it in terms of choice and consequence for me, because BG3 and the writers of it come across as very preachy.
Didn't stop them from going full-on guro/torture porn with a few instances of, well, torture, and a lot of the Dark Urge's interactions.
However, the game's separate bits do feel like they have been written by people with very different vision of what the writing should be like, and they seem to have gone through no normalization of any kind, resulting in a tonal/quality rollercoaster. Like how the githyanki at the creche are written to be as bland and unlikeable as possible despite them being a potential ally against the illithid threat, meanwhile the Thorm/Gortash/Orin trio... or, rather, just the latter two - are all so quirky and "charming" (and somehow attact shippers!) and go out of their way to offer you an alliance even if you make your intentions to destroy them clear as day on several occassions. If anything, I would have liked Thorm to be more than an old man reduced to an arbitrary obstacle no matter whether you sided with the cult before or not, killing any and all semblance of alternative routes through the game.