I play a thief which isnt built around burst but on sustained dmg and elusiveness and distractions. I can kill most players or at least F with them to the point of them needing backup in which case ill use one of my many stealths to hide until backup leaves.
The classes i have trouble with in 1v1 situations is ele's who have a dagger and use the lightning sheild effect on CD, and since i dont have a good dps ranged weapon meleeing them is basically a no win situation for me as ill be stunned if i attack them, i usually stealth and wait for the buff to go away.
Another build is a ranger using traps and i believe melee weapons. That build i have only seen once and not many ppl run it.
And the other was a guardian. I can handle most guardian bunkers but this one had enough offensive firepower to make it a challenge. If i didnt steal his might stacks off him or use my boon removing skill on him (most of the time it misses due to him moving or poor positioning on my part) then he could stun me and get of some good burst.
Thiefs arent all about burst. My thief is about multiple stealths (steal, 25% hp blinding powder, Heal, Blinding powder) as well as making use of thief trap to spawn 2 thiefs as well as the thief elite skill to get 2 more out.
Shortbow to get away (works well when ur stealthed) And useing my surroundings to hide myself. Also shadowstep for breaking stuns/fears etc. Also boon removing skill acts as an evade so if someone immobilizes me and tries to use a burst combo i can use it to evade all the damage. (mesmers and warriors im looking at you)