If someone has one drink too many then drives off to go home, the only intent here is to drive while under the influence. If that person nods off behind the wheel, goes through a red light and takes out a pedestrian trying to cross the street, that is manslaughter. The median applicable sentence would be fine.
If that person, however, was discovered to have had previous instances of DUI, they should then be given the higher end of the applicable sentence - given a history of potentially life-threatening behaviour.
The same goes for this person. He has a history of violent behaviour and it has eventually taken a life. Not what he had intended, but it is the result of a pattern of behaviour. I do not believe that the sentence took that into consideration.