You should have fixed your pathetic excuse for a loot system. On top of that reducing engram drops during missions is perhaps the dumbest thing you have done in regards to Destiny. The reason people farmed the cave is hardly anything else in the game gives rewards worth investing the time in to get them. Strikes can take anywhere from 10 to 30 minutes, and for me anyways the rewards have always been garbage. Redoing story missions at higher difficulty should have higher rewards. Last but definitely not least, the stupid cryptard hardly ever gives something decent, even at level 15+ so before nerfing something, fix the problem not the symptom.