During your first play through the game, Marle is probably the best person to have in your party because she heals better than anyone. Her usefulness begins to go down as you get close to level 100 though.

So yeah, based on whenever I start a new game without using new game plus, I'd have to say that your number one problem is that you don't have Marle in your party. I like Lucca better than Marle, but Marle is just a lot more useful at low levels.