Since the last update the drop rates of the DLC weapons were immensely increased making them drop extremely often. Since you encounter and fight hunters much more often than tanks and harvesters, you will find a lot of AT-WADs and N9s. The other weapons of the DLCs which are linked to tanks and harvesters occur way more rarely.
The harvesters which can drop up to 3 series of hunters make this imbalance more visible. Especially when I fight a FNIX or Apo harvester with up to 9 or 12 hunters I can loot 2 or 3 AT-WADs/N9s but never or very rarely I get a Kotenok or N16. (Not that I wouldn’t care much about the Kotenok at the current state.)
I think this happens because all the DLC weapons have the same chance of being dropped. In my mind it would make sense having lower drop rates for the weapons linked to hunters and higher drop rates for the other weapons. I suggest lowering the drop rates for AT-WAD/N9 to half their actual value and raising the drop rates of the other weapons to the double or 1.5× their actual value. This should balance the findings of the various DLC weapons a bit better.