Why are some actions stuck on left button and right buttons

General Discussion
1

for example, why can’t i use aura on left click on a paladin and attack with right click

2

This is because they are doing two things:

  1. They are preserving the status quo of how Diablo 2 works. Even with quick cast, this is still a two mouse skill game.
  2. They are utilizing the underlying engine to drive this feature.

While it would be nice to have true freedom, and it seems there are some kinks in the system to work out, this is still a huge quality of life. There is still room to improve the feature at a later time, such as when they decide to write new coding to allow for currently right click only skills, to interact with the left click button.