This^^ RNG is RNG, there are no areas in the game where mobs have increased chances to drop engrams. Just because you have a few good runs does not mean it is fact. What if those people that rush through the strikes got a legendary on the strike before or after you and coincidentally you didn't on the next few. Welcome to RNG. The only benefit you are getting from killing everything in a strike is more opportunity for an engram to drop, also it drops loot for the other players in your group. It is a distinct possibility that they went to town and had some engrams in their mail. It only shows they got a legendary in game if they actually pick it up.