So the first issue is feats, this one is the common one. Current feats have contradicted the Mach scaling.
Maki was able to respond and deflect a gunshot that was only a few inches away from her face in this case. Being quick enough, sweep it aside. This demonstrates Maki's ability to respond, move at
Supersonic to High Hypersonic speeds, and deflect projectiles in the BoS. Her ability to respond and move at speeds faster than sound and Mach 3 is demonstrated by this early in the series.
Not only that, but early in the fight Maki
reacts to and cuts bullets that are being fired at her from close range at
supersonic speeds, even after correcting for correct bullet speeds in the other calculation (220-360 m/s). Additionally, there are previous instances in which she s
plits a bullet in two from quite close ranges and
potentially avoids being hit (I say potentially because Mai could have missed, but it does have speed trails in the scene she moved and dodged it).
Fumihiko Takaba's jump into the path of an explosion to halt it, which resulted in speeds of
High Hypersonic, is another accomplishment depicted in the series. This would increase the number of feats for above sound.
Another feat is Sukuna's (3 fingers) feat of blitzing Megumi resulting in
supersonic+ speeds. This feat is important as this same Sukuna is what Toji speed is referred to be
comparable if not faster than, which while still slower, Megumi on guard in Shibuya was able to still react and dodge to him. Showing Shibuya characters in at least in the
supersonic+ ranges.
Yuji dodging Piercing Blood is another feat that showcases speeds greater than the sound. Piercing Blood is an attack that exceeds the speed of sound, while viz says reaches the speed of sound, it has been shown to be an
incorrect translation, viz holds the status of butchering translation in the series. For the Piercing Blood there is a calculation placing it at
Hypersonic+ reactions. The attack is regarded as "fast in the beginning" implying it to slow down after its been fired. However, there is no known rate of how fast it decelerates, which leads to only assumptions. Even if you assume it be half the speed of sound (171.5 m/s) or even 1/10 of sound (34.3 m/s) would still result in supersonic reactions from Yuji.
Yuji at the very beginning of the series reacts to a curse, resulting in
subsonic speeds, only two times slower than Human Naoya's top speed.
There are also other feats such as Geto (Kenjaku) reacting and blocking to
sniper fire and young Geto
blocking bullets. Uraume
reacts and blocks to Piercing Blood with it breaking the sound barrier inches from their face. I've haven't used attacks speeds like
Hanami's Tree as they aren't characters reacting to them, although still showcase speed feats above sound. However, they haven't been calculated yet. There's also a casual Naoya reacting Piercing Blood.