What do you want a thief to do if not sneak around and be all backstabby, lockpicky and so forth?
If you're not doing those things you're not playing that class, you're playing a fighter who insists on wearing leather armor and soft boots!
(Just a guess) He tried to be all sneaky and backstabby and so forth, but the game didn't support that enough so he felt too much like a fighter in leather armor and soft boots?