It's weird, all the modules have been put into logical categories, the modules that protect you from threats were made into ARMR modules, the ones that dealt with detecting and enhancing stealth were in STLTH and the ones involved with weapon control and movement was in POW. What part of Air Stomp helps protect you as an ARMR module anyway? If anything, missing a stomp or trying to hit a sufficiently protected enemy player only makes you MORE vulnerable than anything.
Maybe it was done that way so it could work with [Mobility Enhance II]? Who knows.
Not really a game-breaker at all, it just seems strange that out of all the modules Air Stomp seems to be placed in the wrong category. Heck, even in single player, Air Stomp's a power module choice, what happened there?