You never played WAR I guess...
In melee range, you need GUARD AND HEALS to stay alive. Period. If you got Guard and heals backing you up, you should be able to destroy everything.
Problem with SWTOR as it is now, nobody rolls tanks. Tanks absorb dmg, CC and TAUNT ennemies, reducing their outgoing dmg. Billy ****** MDPS shouldn't be able to survive, rightfully so, but give him a tank and heals that knows what they're doing and you'll see a big improvement.
And therein lies the problem. It seems that no one thinks to use their taunt ability as a tank in PvP to minimize damage, they just want to rush in like Rambo and be the hero.