It all depends on how much time you spend leveling him up, and acknowledging his skills. Unlike the other characters, you have to work to gain Locke's great abilities, and you have to use him continuously to learn to love him. If you just keep him there, focusing on the other characters, then of course he's going to be weak.

I, for one, had to learn this lesson myself. I thought his abilities and talents would come through to the game naturally, but I realized that it doesn't, and since you have to use him most of the time, I figured I would spend time on him, and focus on him even more than the rest of the party, and for serious, it turned out pretty damn well.