Which doesn't match the on-screen visuals and that size chart. We know how small the ENT-D was to an Assimilation Cube, and that the Intrepid class is only half the size of the Galaxy-Class. The visuals of the Tactical Cube/Voyager battle show that VOY is not as small compared to the Tactical Cube that the Galaxy was to the Assimilation Cube. Thus the Tactical Cube is smaller.
So if the Tactical Cube was meant to be an upgrade to the Assimilation Cube, it didn't make it into the show's presentation.