I've played all as DPS and all are easier to run in 4 v 4 DPS matches than vg... Guardian has three lives and a plethora of great defensives; sent has 30 secs of 20% damage reduction, 12 sec sabre ward, 6 seconds of 99% damage reduction, a vanish and a ton of stun immunity; shadows have the ability to drop combat and heal to full, 5 seconds resilience, deflection with spec'd stun immunity, phase walk and shadow step.... vg's have no escapes and can easily be focused down thru all their cd's.
Anyone who actually plays solo ranked knows that vg's / pt's are the easiest targets.
Oh and as far as your guardian dying in two stuns, you're doing it wrong... Focus defense when you get low during first stun, when you get stunned the second time, break it, you'll be white barred, pop your reflect, count to 3 (or 5) then hit your enure and medpak... If you're still in trouble use your aoe slow then guardian leap or blitz to get out and los.