re solution in search of a problem
that's sort of the point: the design is all about validating Mars Direct rather than being based solely on the needs of a mobile robotic mission ..
OTOH an aerial mission doesn't have to contend with all those rocks and craters .. which is why I like the balloon concept so much. Remember that every Martian night, the balloon gently floats to ground, where it does surface science. So, you get the best of both worlds with that concept.