Sorry your experience with the Thief running is so bad. He's always pulled out for me. I should know, since I beat the game at lv. 11 (Was at ToF at level 11. Apparently, we all know that I was forced to 14 before I reached Chaos...), and I only could do it by having my Thief run from nearly all the battles. Fighter wasn't making it away in my game.

Is you Thief failing to run? Or is your Fighter simply getting a chance to run first and succeeding? Because if it's the latter, then that's all it is, and the Thief will be useful on the day that the Fighter simply can't run. If and when that day comes.

AND, when the Thief becomes a Ninja, you'll be glad to have him. Or even once you get him the Rune Sword, he becomes an on par fighter.