You're not quite asking the right question here. You don't want to know how armor and rating are related, you want to know why the Orange item has a higher rating at all, if it's got lower stats aside from the net 17 endurance.

The Orange item, as denoted by its color, supports **item modifications**.

You're right - the base item  is a bit of a wash compared to the level 17 green.

But slot in an Armoring mod, a Mod mod, and an Enhancement mod, and *then* see what comparing the stats again gets ya. It is a higher rank because it has the *potential* for having better stats - it's just that, due to their nature, Orange items require a bit more investment before they're up to snuff.

The system might also just be favoring the +17 stamina bonus - the system thinks 17 stamina is **much** better than 79 armor.