Now a days it may be like that, but it wasn't that originally in the old old days of D&D, then the classes were archetype, but from the progression to D&D to AD&D to 2.x to 3.0 to 3.5 base classes have become more about mechanics and less about archetypes. I am glad for this, it makes the rules of mechanics simpler and more consistent while not stopping roleplaying.