It'd make sense if you actually needed Muga before doing Hyakuren Jitoku no Kiwami... unlike Kabaji, who just up and copied it skipping the whole 'unlock Muga' thing.

Tezuka would win. Atobe pretty much hit a ball so hard the spin was useless on it, but Tezuka puts lots more spin on it than Echizen. Tannhauser serve can be copied by Tezuka anyway... so once he's able to do that, he should be able to think up a counter for it... or just copy what Atobe does.