I think unarmed justice beatings should try to prioritize limbs and the lower torso while having a penalty to odds of an attack targetting the upper torso and head.
It's been a problem for ages. Like, since the 40d days but the new combat and wound system introduced in the DF2010 era made unarmed combat a lot deadlier, furthermore with the pulping changes in 2014.
We often see the beater punching the dwarf in the head which destroys the head, damages the brain, or causes compound skull fracture into the brain, or damaging the upper spine and causing suffocation and paralysis. (or lung bruising)
Another option could be when a justice beating is delivered, the dwarf hits with half force. Might be a little too soft but beatings overall, in my opinion should only rough a dwarf up and potentially require medical treatment for a broken bone or two. Currently, beatings often outright kill dwarves. It's supposed to be a lighter punishment then imprisonment, yet currently imprisonment is far preferable to a beating.
I am alright with a hammerer's beating killing dwarves though. Hammer strikes are supposed to be worse than imprisonment and are effectively the dwarven version of capital punishment.
EDIT: Although I never appoint a hammerer. Reading posts in this thread, violating a production/export order is a hammering? If that's the case, that's pretty extreme. I feel hammering should only be for the most serious crimes like murder, conspiring with criminals, etc.
Pretty crazy the most common crime your dwarfs will commit (being unable to accomplish some stupid noble request because the noble has preferences for stuff you don't have access to like glass on a sandless map) is normally punishable by death, and it's been this way the entire time and we haven't really paid attention because we never appoint hammerers. I think it should be downgraded to imprisonment by default, and only hammering for murder/espionage.