Guild Wars 2

i have trouble to handle some build with my mesmer
i am playing some power pu/power shatter/condi shatter
base armor +2500-2900
dmg when with power build 2.2k base
crit dmg 200%
crit chance 40%
condi dmg 2.1k

weapon used staff or gs with sw/t when power build, and with condition sc/p+staff

as i tried several build it seems its not the build rather my playstyle
ure i can get them to below 50% hp but it seems they have better ways to restore hp and protect themselve than i do with my mesmer

main problems
d/p thieves
med guardian
few hambow warrior

d/p build can sustain stealth and burst me whenever they want. so i cant really react or put enough pressure so the fight goes between 30 sec – 1 min
sometime i can get them down while i am down also

med guard can pull so much aoe pressure blind block and leaps to be on my back while my conditions cant hurt them much

any tips welcome