I'm sorry but thats not as true as you make it seem.
If you master your class, you can always beat the odds.
Sure if you get ganked BY ANY CLASS, and don't have a PvP trinket and/or you're on low HP then you're basically dead. But if you are on (near) full health and have a PvP trinket, I don't think you should then blame it on your class when you die in a WPvP encounter.
So let's say Mages and Rogues are good, cause they can be. Let's talk about other classes vs. these two in a WPvP situation, assuming you know you can get ganked and have a PvP trinket equipped and you have 75% health or above, Ok?
- Paladin: Can always bubble heal, stun, consecrate, cleanse, tank, blessing of freedom, "burst" if ret etc. I don't see any underpoweredness here.
- Druid: Can trinket out of initial stuns, shapeshift out of frost, hot's and dot's, sprint, (warstomp if tauren), tank, kite, roots, burst etc.
- Warlock: Can trinket when needed, death coil, fear, dots, drain life, summon infernal if high enough level, seduce, magic absorption, nuke, felhunter purge and paranoia.
- Warrior: Can equip shield + 1h, can tank melee dmg, can trinket, burst with 2h, shouts, bleeds, 1 intercept, hamstring, I will say against a mage its gonna be very hard but hey thats anti-class everyone expierences that sometimes
- Hunter: Can trinket, could pet stun/snare, can trap, feign death, burst, dots, hunters mark, melee and ranged, kite, mana drain, run with aspects; dodge with aspects; burst with aspects.
- Priest: Can trinket, fear, shield, hots and dots, mind sear, mind blast, heal, vampiric embrace, more hots and dots, has stamina and armor buff, shadowform increases armor etc. aswell
- Shaman: Can trinket, earthbind, frostshock, heal, flameshock, interrupt with earth shock, grounding totem, burst with 2h WF, fire totems, anti-poison totem, stoneskin vs. melee
What more can I say?
As long as a good dps class has the jump on you, you are likely to die unless he sucks and you don't.