Yep, head hunter isn’t good choice against heavy armored knights, orc warriors, warlords and encient guards. As I said, it’s a situational thing, but actually, in the latest patch you can meet orc warriors without helmets and they are really easy to take out with flail.
The Headhunter is as bad as Fast Adaptation is, if you think in that direction, the better your hit chance gets, the less you denefit from it, don’t you?
But this are some early game perks to work with low skilled brothers and weak enemies. Sure, I doubt it’s a good idea to take this perk for your hedge knight, you have better options. Also, it works well with archers, because enemy archers rarely have helmets, so kill two or three of them in one turn becomes a bit easier.