My understanding is that it went like this:
3.x: Casters are gods, martials are muggles. There is nothing resembling class balance.
4e: All classes, martial or caster, are demigods. Classes have comparable resources, and excel at different roles.
5e: Back to 3.x framework, except casters are demigods with limited resources, and martials have limited access to their 4e features.