You are confusing features for content. When you bought the game and its DLC you bought the content not the features. The nightfall has always taken the latest level-cap into account and then amplified content to that newest cap. That is exactly what its doing now. Its taking the latest cap which is 40 and amplified content to match that new cap. The same goes for the weekly. The same also goes for the Crucible. The game modes took the content that you paid for such as maps and guns and adjusted them to fit within the confines of that game mode. The same is happening now. You have not had any content that you paid for taken away from you. The content that you paid for is simply no longer featured.