What would a Zeronaut be? Sounds interesting.
Those titles sound good. I think the problem with trying to "generic" them is that titles really are defined by their setting. A "fighter" can be called so many different things by different cultures - samurai, bushi, warrior, swordsman, man at arms, speardane, etc., etc.
I like your sci-fi names. They do sound pretty cool. And having the thief as an investigator is a cool idea.