If you want to kill big shit quickly, go with gally. For everything else, anything will do. Like someone else said, gally shines in clutch, very important moments in raids and strikes so when it shines it shines bright. No gun is absolutely necessary, but you will be glad you have gally when Oversoul is active, Crota is at 10% health, the sword guy is stepping on his toes, and Boomers are raining white hell upon you.