You know, all the way back when Larian first revealed Kethric Thorm in a trailer, people said he and the other three would be more like secondary villains, that Larian was spoiling them because they would be working for some big, true antagonist that's kept unrevealed. And they were right... and they were wrong. The "true" antagonist barely matters, the chosen three barely matter, I agree that the story problem is well beyond just act 3, it's a culmination of other stuff that started well before then.