if you run classed npc vs. monsters I see where fireball stands out more.
another thing to think about is where most of your combats take place, while I dont think fireball's spell description said anything about setting things on fire most of the player I play with use the logic (kind of a house rule) if you use fireball inside of a building or in towns chances are you are going to set the building you are in on fire or the town so they tend to stay away from fireball unless they have too.