I disagree.I think objectively, and in this point in time, the best argument in the officers favor would be to say that his training overrode his judgement. Maybe because of the struggle and his pursuit of Brookes he was in fight mode and he was trained in escalation of force that stressed going from taser to pistol when someone pointed a weapon at him. I actually think this is what probably happened.
Anyone who has been in a stressful situation knows its very difficult to switch back to a normal state.
The best defense the cop can use IMO is to say that in his judgement, he was in fear for either his life, fear that serious bodily harm would be done to him, and/or his judgement told him that the public would be threatened with the same. Then he followed the procedure of what he was trained to do.
Maybe he was in the fight mode? Could be, but it had nothing to do with his judgement. It had everything to do with Brooks punching him and stealing his tazer. Did he look like he was in fight mode before Brooks resisted? He set out to finish what he started, and that was to arrest Brooks using whatever force it took to complete that task.