I dont know what assassin class your playing, but dieing alot in pvp? out of all my characters i find assassin dps is the best ive played in pvp i rarely die. And as for light armor tanking, makes no difference, dark charge gives you +150% armor bringing you on par with heavy tanks. Not only that but as it stands guardian/jugg tanks arent the greatest at tanking more then one mob, Id take a assassin/powertech tank over jugg anyday. I played sin tank up to 40 before switching to dps to give it a try, and tanking was a peice of cake
Maybe your gear/skill as a assassin is just under par idunno, but all in all id hardly call it a bad stealth class.