For example, old D&D is pretty well balanced, the thing is, combat is not the only measure of balance.
Party line up 1: Fighter, Fighter, Fighter, Fighter.
Party line up 2: Cleric, Cleric, Cleric, Cleric.
Party line up 3: Thief, Thief, Thief, Thief.
Party line up 4: Magic-user, Magic-user, Magic-user, Magic-user.
Party line up 5: Fighter, Cleric, Thief, Magic-user.
The most effective party is the last one. When people say "wizards rulez" or "cleric rulez", an all cleric or wizard party is very uneffective. Game balance comes from the fact that each contributes to the adventure , something much bigger that just combat, in a meaningful way.