Technically, most "Kamados" should be called Mushikamados if we're going off of the original Japanese terminology. Kamados were stationary while Mushikamados are considered movable. But, the material used to make the cooking device isn't strictly limited to one specific material type, although the original Kamados were typically made of unfired clay.
Does the Kamado Joe II use charcoal as the fuel source? If so, it's generally going to be categorized as a charcoal grill just like the Summit Kamado, so I'm not sure how sure how calling the Summit Kamado a "glorified charcoal grill" is a negative.
And, the WSK has a 24" diameter cooking grate vs the 18" on the KJ2. Plus, the WSK E6 is 110 lbs. lighter, so it's much easier to move. It's also more forgiving if you overshoot your target temperature and need to bring it back down, and it'll never crack.