I totally understand what your math stand for, glad to see that you have made your great effort. But I have to say There is little flaw when you calculate the min value of armor you still use the same formula while it ought not to.
But this is not the point right？
Like you have found out, fearsome only barely relatively useful for support guys like shield man or billman, it doesnot match it position in perk system as a terminal perk. That the point, it should get accessed earlier.
And another point, fearsone not meant for low anti-armor weapon, maybe it should be ignor armor correctly. With duelist build even sword can cause 15+ hp againt opponent with 200+ armor let alone named sword.
So actually, conclusion maybe, only support guy need it, and support guy is always lack of perk I guess.