Either way, you have to get lucky to get it. It's not in our hands. You don't have to fight some extremely hard boss with a guaranteed ghorn at the end which you would "earn" it through. I've put in plenty of hours and help people with crota and vog every week even after I don't need the drop. Plenty of people get it but I still don't have it. Kind of ridiculous. I've talked to two people in the last week who have 4 or more.