EQUIPMENT RARITY

Good evening.

So, what do you people think of equipment rarity?

Some stuff didn't quite fit for me. Some items are classified as ultra rare etc., yet, you can buy them, craft them. At the moment you can simply buy something like that from a merchant, I don't get even why it would display a rarity quality about it.

I miss something unique, some unique equipment dropped from enemies, found in a hard vault. More into the game, these rare qualities don't have a seemingly definition, nor use.