Quick note that bank switching does not in fact allow the CPU to "address" more than 64K. It allows the machine to "have" more than 64K but only 64K of it can be addressed by the CPU at any time.
What makes the CBM-II's 6509 fundamentally different from the C128's 8502+8722 combo? And what makes either fundamentally different from the segmentation scheme of the 8086/8088?