I have an idea that would make AST more desirable to take.
What about making Celestial Opposition stop the time. Instead of stunning the enemies it would froze them in time (including all bosses). It wouldn't interrupt casts, it would just froze them and after it finishes the freezing the cast would continue.
With this change the skill would become the ultimate ability for AST. You could froze a boss to set up a mitigation strategy and minimize damage. You could froze the boss to let your team dodge that AoE. You could froze that boss to help your party to recover after a big unavoidable damage. You could froze that boss that's about to enrage and give your party 4 more seconds to kill him.
