I think the item quality should affect more than 1 value.
in case of the leather armor:
low quality armor have 1/1 and 100hp
medium have 1/1 and 200 - 300hp
high quality 1/2 and 300hp
nearly best quality 2/2 and 400hp
something like that.
that would be a really incentive to build up better and better quality leather armor.
if better quality only increase the hp, everyone would make a iron plate armor instead of trying to get the raw materials to craft a better leather armor.
this would look so boring and monotonous.