Mind you, this was tested under FO2. I still have to try it in FO1. (Last jinxed FO1 guy I played had 1 luck also.) For one, high luck only shields you from critical failure, not failure in general. I still lost all ammo, dropped my weapon, and lost my next turn. The last one was usually more deadly than any critical failures.
As for game balance, this is just anecdotal evidence. It seems like they tweaked Jinxed in FO2. The enemies seems to have made less failures compared to FO1. There was still failures, but not much. I can try to outlast \ outluck them, but that usually winds up me being dead from missing turns. And this is on LUCK set on 10.
I think I know what you mean though. Here is my personal take, served with a bucket of salt.
A Jinxer with high luck is no more stranger than a Small Framer with high strength. And there is a real life example for this. Many powerlifters (deadlifters?) have compact frames. Just looking at them, most would never guess they lift ridicilously heavy things on a regular basis. One powerlifter from a few olympics ago was nicknamed " The Pocket Hercules."
But how could a Jinxer have high luck?! It seems contradictory!! Not that contradictory IMO, Jinx is a combat specific quality, while LUCK is a general trait.
A character might be unlucky in combat, but quite blessed in a game of chances. So the whole universe is against him on the battlefield, but lady luck loves him on the craps table.
Hmm, this whole discussion makes me want to start a luckless Jinxer again. Last one I had kept on dying on the way out of Navarro base.
* By the way, I saw Fallout Tactics for 20 bucks. Kinda interesting. Maybe when I get my new comp I'll pick it up. It has multiplayer...