Like some others, I think the Rogue is too good. However, I hate the idea of the Rogue losing his high damage potential.
My suggestion is to tone down the Rogue's ability to kill higher level enemies by lowing his damage bonus but giving him Reflexes as a passive. This doesn't hurt his damage output (I think? Assuming he has -30% bonus damage), but it does mean he will struggle to kill things that he can't take at least one hit from.
This might be a significant nerf in a lot of situations, but it would allow him to override First Strike (since Reflexes has maximum priority now), giving him a niche.
Perhaps the health penalty could be scaled back a bit if this makes him too weak (or maybe he could get Dodge prediction back).
Thoughts?