LOL
There's always possibility for mage to beat rogue or warrior in duel mode, thats the challenge and very interesting try and try again to check how the weak mage could beat another class.
Just try to duel with another class, you'll learn then you can kill some..
But for now, yes, mage the weakest player in pvp even rogue and warrior said "mage are hurt and scary". In their heart "how easy to kill you" hahaha
It doesn't matter you put shield earlier or later, the problem is it can be broken less than 5 seconds if your enemies so hurt and do critical