You literally have 3 nightfall chances, 3 exotic vog chests, 3 atheon exotic drops, 3 it yut exotic drops and 3 crota drops per week to try and get it. 15 chances at a shot at it. Keep playing, it'll drop eventually, or you should have been around at the start and picked it up then. They won't nerf it because it only makes the bullet sponge bosses drop slightly faster. It's not game breaking in the crucible which is the source of all nerfs. Pve is not hard, it's a repetitive grind, the only thing ghorn is good for is dps on bosses. And even then Black hammer can technically out dps it on slower/stationary bosses with big crit spots. Sure on solar burn night falls it wrecks, but those are few and far between and that goes back to my black hammer statement.