His opinion or my opinion or your opinion doesn't matter. What matters is the law, and what the law says about when deadly force can be used on a fleeing suspect. If Brooks does not meet that criteria then his shooing is not justified. And the criteria is did Brooks pose a significant threat of death or serious physical injury to anyone? He did not.
The film talks about Rolfe seeing Brooks fire at him. Well Rolfe had to know that all Brooks had was a Taser where one dart had already been fired. Once Brooks shot the second dart then the weapon was no longer a threat. Rolfe shot after the taser had been fired.