Probably because you're only in sxs lvl 1 one time in the whole game ever..and in lvl 3 the taunt ss more used for giving space to you and your opponent if you actually want to use it...
Are you getting the full damage from the 66B+K? I'm sure it does more damage. X has to step once after the launch for her to get the full damage from 66B+K after FC3B