A wheel can be perfectly balanced, but not round. As in elliptical shape rather than perfectly circular. Roundness is one of the things that manufacturers specify tightly for OEM parts (ones delivered new on the car, even if someone else actually manufacturers them). You can also get out of roundness from mistreatment. Some manufacturers deliberately specify a soft alloy for wheels so that the wheel bends rather than the shock being fed into the suspension components or chassis and bending them.