I agree with a lot of stuff. What I can add is, that I'm really struggling with the narrative structure. I get the odd feeling that the game was planned to have 5 acts that had to be compressed into 3 for unknown reasons. Act 3 feels a lot like a middle part, instead of narrowing stuff down, the game opens up and I get side quest I would expect early to mid game.
Honestly I completely agree, but I am having a hard time pin pointing the exact moments that need fixing, all I know is that the story started to make less and less sense from the moment the Emperor reveals himself and you are forced to take his side.
To your point, in act 3 for example you are just bombarded with quests that want you to run in opposite directions and have no impact on killing/siding with Orin/Gortash, it is so strange.
*Edit*
It is also strange how the narrative peaks at act 2 and act 3 just, is not engaging. Maybe if 4-5 acts were planned it would be sufficient time to build momentum towards another peak.