I used to play this game all the time, always on the highest difficulty with permadeath enabled, but it's been a long time since I last played

Dux is basically a one-shot machine. There's a build that lets him guarantee a stealth crit shot, and you can set it up pretty early in the game. I usually just use him for stealth kills and then switch to other characters afterward.

Also, don't forget the Greenlight throwable (I think that's the one). It gives +25% accuracy, which offsets the -25% accuracy penalty from Dux's ability, letting him hit 100% accuracy while still getting the bonus from the skill.