The Agent/Smuggler class dominate in pre-50 PvP because they scale very well. Once you hit 50, though. Well, you'll figure it out.
You've gone from being the big fish in a little pond to little more than a targeting dummy.
Yes this pretty much sums it up. And on our server, where Reps dominate, it's even worse. When you go up against a team that is all War Hero geared, then your damage will be extremely mitigated. After I got to 50, it took a long time to get that 5K medal and the first time I did get it was on a sorc who had low expertise. The Reps do sometimes have a guy a in full Recruit and I was always happy when I saw those because I'd think finally someone I can kill with ease, but the Reps do such a great job of protecting him that I was just getting myself stomped trying to kill those guys. When you have to go through a War Hero healer and War Hero vanguard to kill one Recruit smuggler, it's just not worth it.