It will make everything in the game ridiculously easy if everyone has one, that is the point of this post. However, as it stands, simply having one Gjallarhorn in the team is not overpowered. Once you get two or three, raids become a bit too easy. So who knows, maybe it could use a patch, considering how deadly those wolfpack rounds are. But until that hypothetical patch happens, Xur should not stock Gjallarhorn.