Fifth'd actually.
Having watched it again in slo mo it is very clear that every one of those blows connected with his head, AND he has been throttled, AND it was clear that the lunatic thug was not going to be kept down by the tasseling and was already coming round. Plus he had to prevent either of them from taking his firearm.
So that's an awful lot of mitigation, in fact.
If you want cops to think clearly and act by the book, don't try to give them a head injury or compromise their oxygen supply, is the lesson.