The witchblade is intended to keep the balance of power equal between the darkness and it,s bearer and the angelus and it,s current host. So there are times when the witchblade can equal or overpower the darkness or the angelus all to keep the two prime forces in the witchblade world on a equal footing.
Yes the witchblade can cover the user in full armour in the later comics it stops being a metal bikini and becomes a little like a combo of both the darkness and angelus armour. Remember it,s a female character the more chances to depict her nearly naked the better.
The lore says a male cannot bear the witchblade but there have being a couple of users the medievil one shot shows what happens when males try to bear the blade iirc but no a male cannot bear the blade.