I'd argue, that the D&D setting does not easily lend itself to though-provoking and nuanced story writing, especially if its mythology is taken at face value. It has a bunch of evil creatures, evil gods and even evil races that are evil just for the sake of it. Unless the writer is willing to critically deconstruct the tropes of this universe there is little possibility of a story that could engage the adult mind. With brilliant writers everything is possible, of course, but BG3 is not written by geniuses. The main story is shallow and even ridiculous at times. BG2 had Irenicus as main villain, an interesting and somewhat relatable person with complicated motivations, BG3 has the EVIL Elder Brain monster who is all about DESTROY!
The game is best enjoyed by completely ignoring its story.
By far the lowest point of the story is the Emperor promptly joining the EEEVIL Elder Brain, after the player choosing to free Orpheus. It is so dumb, it hurts.
