There's no Linear Fighter, Quadratic Wizard* - every class is balanced and there's no "I win" button for the caster who prepared for the encounter. Because you can't "prepare for the encounter" by having a load of spells ready.

Every role has a function in combat, and better (ie more effective) parties have all four covered. The best party is not four Wizards (they'd get murdered) or some other arrangement like that.


*Wizard being a catch-all for full casters in 3.x