So let me get this straight, your argument is that Dragonbone cannot be made into weapons because they make good Armour therefore there properties surely cannot make deadly weapons, and to back it up your argument is 'Armour is not a blade'...
Let me take you into the real world and the basics of Skyrim:
Steel can be made into armour... can also be made into a blade
Ebony can me made into armour.... can also be made into a blade
Any smithing material you name can me made into Armour... can also be made into a blade
Therefore, even by infant intelligence, it is safe to assume that even though Dragonbone can be made into armour, it could easily be made into a deadly blade.
*clicks fingers*
EDIT: I feel evil after writing this.. i think my internet rage kicked in... sorry xD