The story quests aren't necessarily well balanced but I agree that Thieves could use some love. I still love mine in PvP, I'm an unkillable asshole who frequently distracts groups of 5-10 people from an objective while my team goes after it.
That said, I have a Warrior in the high 60s already and its far more enjoyable while providing more DPS and arguably utility in PVE content.
Playing: Dark Souls 2: Scholars of the First Sin Watching: Mr. Robot