Outside of their small trap-finding door-unlocking niche, being fragile as they are, what little else have is sneak attack, while some could argue that it is strong as it is, the ugly is truth that sneak attack is the only thing to compensate for the many weaknesses of this class.
What I would ask is nothing but having sneak attack behave just like in D&D, just one thing and more exactly;
- All eligible attacks from a thief even those from the off-hand should be a sneak attack if they are eligible for it
Just that, perhaps this modification with lift many of the hardships found with this class.