i had this EXACT same problem with my ati.
i ran guild wars 1 login screen in the background to fix it(forced utilization of gpu. went from 20% to 80%) then upgraded to a nvidia.
light 20%~
medium 25%~
heavy 30%~
it matters, but not by much.
survivability is determined by defensive cd's, talent points, and tanking stance.
the squishiest class in the game is wearing heavy armor fyi.
without railshot every 6 seconds your effective damage is trash.
pt's get to spam flame burst. mercs have power shot. if you're not trying to get your rail every 6 seconds you're the same as a pt that has flame burst removed from his bar, but with a weaker rail.
this 100% mobility is severely hurting your damage.
what assault has over arsenal is they can still do mediocre damage while a melee is on them.
a good bit of sorcs damage is still mitigated by armor. only their 2 weak dots and deathfield is not.
a majority of their damage is still lightning and crushing darkness.
watching streams and 2.0 ttk is half of 1.7. powertech is EXTREMELY strong, critting for 7k.
he is dueling a sage healer and killing her in under 5 seconds.
there will be some major balancing before the expansion goes live.