Add a lack of cool light and finesse weapons.
In general, allowing essentially 4 attacks per round as a thief makes them kind of OP. Play a STR based rogue and for level 4 take the 2 weapon feat giving 1 AC and removing the Light requirement. So you have four d8 attacks. Main, Off, two bonus. Also, make sure your best weapon is in your off hand. Add fire for another 4d4. Add possible sneak of 2d6. Add weapon bonuses. Add +3 for strength, etc. It's the highest damage in the game.
