The “standard” definition of a WCD is a 6WD drop-center, cantilevered wheels, live-axle, center directly driven off of the gearbox (usually a 2-speed gearbox), outside wheels chain-driven off the center axle.
I don’t necessarily agree that WCD is the best of the tank drives, partly because it does take some precision to make and thus might be rather difficult for some teams, but it is up there if a team can build it properly.