I agree with the cringing part, most of his performance makes me cringe, I think you can leave the scene as is in your edit, just put his voice over the transition from the backside of Anakin to the shot with Mace with his lightsaber raised. Mace almost pauses and moves his head in disbelief as if Anakin is still speaking so it may work. ( I also realize it may not
) Maybe even simply replacing, "you can't" with "I need him". By itself, I don't think it will be as cringeworth, especially if we're not SEEING him say it. I just feel we need to see a little more emotion from Anakin before he lops of Mace's arm. The Anakin and Padme scene, I didn't realize you had left it unchanged...It's been a while since I've seen it. I agree with you about the emotion part, I think it's one of the most impactful scenes in the movie, I just think it could be even better with a little tweaking.