A haki user would focus all his power on himself. Coating a weapon takes a bit of his power, but covering a mass wouldn't spare him enough haki to protect himself, and even if Doffy did, his haki won't be that dense to protect him. There is no way that Armament haki density is the same. Think of it as like honey. More water, more lighter the honey becomes. Luffy's G2 couldn't hurt Doffy because Doffy's haki was much denser, means much higher. The only way to break Doffy's haki is more power. That's where G4 came for that purpose.buggy can but what if doffy infused bird cage with haki,then logias could not get out and even if they did theyll take dmg.