Think about it. The mighty Gjallarhorn, obviously it's a very effective weapon, so why do people want to limit the amount of other people to own it and use it effectively? Why make things more difficult for yourself? If your team members had the Gjallarhorn, your missions, or strikes, or raids could possibly be much quicker and much less stressful. The Icebreaker is another example of a weapon that people wanted to keep exclusive, but it had recently become readily available thanks to Xur. Everyone has benefited in one way or another from the majority owning the Icebreaker, even if you haven't realized it yet. ...And the game did not break because the Icebreaker faded from "exclusivity". It got better. Not unlike Xur possibly selling the Gjallarhorn. The game will not be broken from the majority owning it. It will get better.