The big difference with those instances is that he was justified in doing so those times. The Mando senator was going to blow up a ship, and Trench had started electrocuting him.

Dooku was literally unarmed. I don’t disagree that Anakin would brutally go for it immediately, but he’d recognize afterwards how unjustified he was this time. It’s too far, even for him, but especially for a Jedi. I think recognition of that, and seeking justification/validation for it (from Palpatine) is essential to his arc.