I mean it is not D&D. Lore wise it would make no sense to limit magic to daily use.(weak excuse, I know) The best way to balance magic is to not even allow such powerful spells. That is why DnD is so unbalanced. why play as a warrior when by level 10 a wizard is going to summon a squad of demons and throw town destroying fireballs.
AOE magic should have a cast time which adds a risk to casting as enemies could move out of the way which is why you have warriors restrict their movement. But again. "Fire armageddon" would not be a spell. The spells have to be kept to immediate combat spells as larger more powerful spells would not be feasible to use. sure a very powerful mage could level a city with a "Lava font of mount doom" spell. but it would take several minutes to cast. Think of Dragon ball Z. Goku could defeat all enemies with spirit bomb but that takes too much time.
That is how I feel Magic should be treated. weaker combat spells should be a focus.
A game that gets this right is Fallen enchantress. You get almighty spells that you can use on the campaign map to destroy cities and wipe out armies. but on the combat map you are stuck with Fire dart, Shocking grasp, firestorm (which is only a few meters) ect.
