The moves would be based around their ARMS. Every fighter can use every ARM. Those four Arms characters can reasonable do all the same things. they aren't heavy weights, they don't have abnormal bodies, they don't float. For character differences, that's already been rendered moot. By being in Smash they would get access to multiple jumps, Aka Ribbon Girl's special ability. All characters with multiple genders have themselves be equal in physical proportions of their counterpart despite have some differences. The MK ninjas grew to get more unique traits as time goes on, but they all started with similar move-sets. And With Byleth, Nintendo has shown that separate animations can be done for differences alts.