Really Bungie and MSFT... WTF? It probably would not matter much if it weren't for the fact that the only platform I can get onto XBL right now with is through the 360, otherwise I'd be playing it on the Xbox One.
That said, if I have a valid/legit copy that to this day works on both the Xbox One and the 360, are you -blam!-ing kidding me that I have to buy the DLC twice in order to have it available for both platforms...
I'm honestly NOT surprised that you have it set up this way. Not in the least...
-
Have you tried the #help forums?