You can click 'edit post' instead of double-posting. Double-posting is frowned upon here ;)
I don't think putting points in defence is gimping yourself, dps is just one aspect of combat. The point is that you need to be able to down their life faster than they can down yours. If they can down yours super fast, it doesn't really matter that you can down theirs fast because you'll be dead before they are.
Most of the time even in PvP, the best builds will have a mix of defence and offence. That was true of basically anything I played in GW1, I doubt it's any different in GW2. At first, while people learn, high-dps builds will be pretty good because other people will likewise not bring defensive skills. But pretty soon people will learn to survive and high-dps builds will drop from the meta.
Thief has skills in the optional portion that also grant stealth or defensive options. Pistol/pistol can be traited to apply cripple afaik which is a good way to deal with melee opponents. Stealth is also not the only way to defend yourself, you can blind the opponent for example.