I wouldn't say terrible damage, but I get slaughtered if I send Kira off to sell items and I need to take on more than one mob. Maybe I haven't perfected the right leveling rotation or something, but unless Kira is on her game, I don't do so well by myself.
With that said, I really have no qualms having chosen a guardian. I know that at level cap I will have an important role and until then I am chilling with DPS for leveling. It doesn't seem to be a great tree for the class but its certainly fun. I just wish I was getting better gear for questing, I seem to be replacing things very slowly. Actually more recently its been picking up with quests from Nar Shadaa.