As armour is the only piece of equipment with no bonus, there is never a reason to use one that’s less powerful. With the other equipment sometimes you use a rare over an epic or an epic over the legendary for the effect/red dice. Perhaps resistances or statuses can be added to armour. Immunity to injury, dominate, stun, etc. Each level of armour could have an immunity or two (epic/legendary). Status effects could also be used, fury, regenerate, block, etc. although the wondrous item also does status effects.