Basically there are some awesome unique armour sets in the game that give decent bonuses when you wear 2+ of the same set, the problem is when you get them they scale to your current level. This combined with the fact they are ultra rare means by the time you have a whole set, you've gone way up in level, the unique armour is matched to your old level and the new generic armour is out classing the unique armour.
The developer is admitted it is a bug and is looking into fixing it. Some armour sets wont even spawn at all with the current loot tables. :
The lead developer actually posts on the steam forums, you can find more info there.
I good way to get decent armour is to max out sagerafting and blacksmithing. Salvage as much as possible and craft your own equipment. I myself am using the Theives Guild armour. I waiting until later in the game to complete the quest which gives you all the armour in one go.
Another tip, is if you get any pre order armours (Mass Effect armour, DLC armour and weapons), don't open the pre order chest in the first town until mid to late game. Equipment scales when you open the chest, not when you start the game. I wish I did. The Mass Effect armour and Omni blades look great IMHO.