My viewpoint is that exotics have their times and places. Gjallarhorn is excellent for raid/strike bosses, complete overkill everywhere else. You could be using an exotic primary or secondary and be much more efficient. Ice Breaker is pretty awesome almost everywhere, but Black Hammer is just as good if not better, and is only legendary. Similarly, if you're not in for the long run, other snipers will have higher DPS by virtue of reloading faster than IB can charge. Thorn/Regime/Mythoclast are ungodly in the Crucible but they don't run strikes on their own like other weapons can. But when you're faced with hordes of trash enemies, for example the first 85% of all strikes, nothing brings consistent success like Bad Juju, and reward that success with bonus super energy for the latter 15% of said strike.