No seriously, how come do you come to this conclusion? When one says superhuan, the first obvious answer should be Hijiri.
Because of time-slowing gimmick. As Marisa says, "when Youmu prepares herself, tension runs high and time seems to slow down for everyone" or something similar. Byakuren is superhuman (like 99% of the named characters), but doesn't cause anything of the sort.
It's time... I can do it!*Shake*Power Levels are... rising... Power... overwhelming...UwooOOOH!OooOOOH!Gwoooooh...Ooooh... OoooOOH!*Tremble*