I thought exactly about that, I fall asleep just thinking about it. Only time when he was dead pan fighting was while Robin rescue and Water 7 beaf with Luffy, but while it he have had to things on mind: fact that he don't want to kill Luffy and fact that he has to be careful to not hurt Robin. Loosing another parent, parent for whom he waited YEARS to even at least see again, after whom whenever there was occasion to hear about is he fine or such, parent who as we see under crew's pressure or not came to see him, will straight up snap the rubber band in him, letting out all emotions to leave only wrath to get person who did it.