Generally I agree pretty much with what you sad so just few things coming to my mind in response to your points:
1. Some enemies are just being asked to be head-shotted. Up until you reach lategame, plenty of enemies wear little to no headgear. The weasel guy in the tutorial oddly is one of them – don’t think I’ve ever seen him wear head armor. In the late game though, only Sergeant, Berserkers and geists come to mind. All are very deadly though, geists die in one hit anyway.
This is true of course, however by the time you develop head hitting specialist, most of these “early” targets case to be the issue, therefore I am not sure if cost in time, perks and money invested in such a guy are worth it. Developing specialist and babysitting him only to find his talent to be actually counterproductive (since he will be actually worst against targets with armor then your other guys) in most cases by the time he reaches full maturity is dubious.
2. Nazghoul thingies never have armor. Hitting the head is always better. Werewolf armor is arguably weak enough to make the same reasoning.
This is true, unfortunately in both these cases spearwall is more effective in dealing with them then hitting their heads. At last most of the time.
3. Sort of related, flails and axes are generally useful for the Ancient dead’s frontline troops. They have shield wall every turn, have infinite stamina and maybe even have shield expert. However, their shields are shockingly fragile for late-game troops so one greataxe specialist smash always breaks it. You’re meant to either break the shields, use flails to ignore the shield defense. I think it’s probably better to use reach weapons/greatswords to hit the priority targets behind them though.
True, but then again, you don’t want to distribute hits over their head and body. So flail yes, but you want it to hit body, not head.
4. Duelist builds. I wonder how much damage we’re looking at for an axe head hit from a duelist? What if the brother has the brute perk? The idea is to kill the enemy under the armor before the armor breaks, so head hits may be always welcome. Alternatively, 2H weapon may kill before armor is destroyed if you keep getting head hits with a brute, particularly 2H hammer.
Duelist and crossbow expert are the only cases where I tend to think that increasing head hit chance might actually be useful. Although I have doubts even here, since in lot of the cases, perhaps majority you are using more then one brother to attack one enemy. Unless they are both duelists or crossbowman, you might loos some effectivity since all other brothers will still be chipping through his body armor.
One more specialist I tend to think increasing head hit chance might be useful would be dagger specialist using special attack which bypasses armor. Yet again, daggers themselves doesn’t give bonus to hit the head so you wouldn’t get as much out of it as with flails.
Btw.: many if not all 1tile range 2H weapons hit both head and body during attack, so I ques increasing hit chance with them is pointless. Or?