Wario's ground game does get a boost when he unleash the tire ****. He gains frame advantage whether you shield it or you it hits you directly. And with proper positioning, they are very threatening active hit boxes when they bounce; requiring you to give up space or respond to the tire. Like I said, by default
has a better ground game imo. When Wario get's the tires out, it shifts over to his advantage. Neither character's advantage in this department is staggering though. Their ground games are just too lackluster as a whole to REALLY shift the MU dramatically in anyone's favor. Ground vs ground battles are not going to be that common in this MU anyway.