I don't care if it's boring. Statistically speaking, you're wrong. Your chance of getting an engram is 10% give or take...You're taking 10% on 20 mobs vs, 2-3 GUARANTEED engrams on completion. If you want to stand there and kill trash for a 1% chance of a legendary engram, that's your prerogative but, you're wasting my time since it's now guaranteed at the end. Mathematically speaking, the rewards for completion are better than your farming those mobs. Period.