The stone axe has the same attack damage as a diamond axe (9), which is also more than a diamond sword

In the latest update (Minecraft 1.12), the stone axe has 9 attack damage, which the same as the diamond axe more than the diamond sword (at 9 and 7 respectively). Therefore making the diamond axe useless as a weapon. This does not make any sense as the stone sword has less attack damage than the diamond sword and the stone and diamond axes should be similar.