I really enjoyed Dawson's flamboyant summation for the prosecution. Humbert Allen Astredo really seemed to be enjoying himself--I've always loved his expressive use of his hands. Barnabas probably should have done all the things you suggest, Lydia, but I think his rather economical, restrained summation for the defense was intended to be a contrast with Dawson's.
It certainly was a contrast... Barnabas's summation, while technically correct, made Quentin and him sound guilty as sin. One could almost interpret his remarks as gloating over their having eliminated any possible opposing testimony.
I like HAA in the courtroom too, and while I generally don't think of Dawson as a distinctive character, I've noticed this time around that Dawson raises his voice when he's especially driven to do or express evil, even when he doesn't want others to know he's evilling. He shouts in an alarming, jarring way beyond how anyone might speak in a normal everyday conversation. I like it.