Here's why I believe having weakened shigarakis hand/arm movement in the final war as subsonic is a ridiculous lowball and hypersonic would work way better as a safe lowball.
First I'll explain why subsonic wouldn't make sense and then I will show my reasoning for hypersonic
Here we can see a much weaker 75% shigaraki blocking endeavours punch with his arm, meaning that unless you think this 75% shigaraki is faster than final war weakened 100% evolved shigaraki that his hand/arm movement speed is much faster than subsonic
Here we see again a 75% shigaraki moving his arm/hand at over subsonic speeds and dodging one of endeavours strongest attacks
Here we see a 75% shigaraki that's literally getting burned by endeavour hitting endeavour with a blast from his hand before endeavour could react
Here we see again a 75% shigaraki almost catching endeavour by suprise with his arm speed as endeavour himself exclaims how impressive this shigarakis speed is RIGHT AFTER HE GOT BURNED.
Here we have a shigaraki that had just got seriously damaged by endeavours vanishing fist speedblitzing Gran torino with his arm/hand and grabbing him.
And here is literally an extremely weakened 75% shigaraki grabbing a 100% dekus face with his arm/hand. So unless you think that an extremely weakened 75% shigaraki is faster than a weakened 100% evolved shigaraki you must accept that susonic speeds are a ridiculous lowball.
Now here is why I think hypersonic works better as a lowball and is more realistic and creates less plotholes.
Here we have an extremely weakened 97% shigaraki jumping from aircraft to aircraft without a problem and dodging projectiles fired from those aircraft which have to inherently be faster than the aircrafts they are fired from for them to move forward. The fastest aircraft irl is hypersonic in speed, mha is way further ahead in technology so those jets would be way faster but hypersonic works as a safe lowball, specifically 2,020.621 m/s as that's the fastest irl.
We see again extremely weakened 97% shigaraki outspeeding those hypersonic aircrafts by a lot.
And finally here we see in these 2 images that in the first image shigarakis both hands are down and immediately in the next panel he's right in front of sns with his arm/hand straight forward. Which means that shigaraki moved his hand/arm staright up as he was moving at at least hypersonic speeds towards sns.
All of this I believe shows that the completely arbitrary subsonic speed for weakened 100% evolved shigarakis arm/hand speed is a ridiculous lowball that doesn't work and creates problems. Hypersonic speed, specifically 2,020.621 m/s, works way better as a safe lowball seeing as shigaraki has constantly showed above subsonic movemant with his hands/arms even when extremely weaker and weakened while weaker and easily outspeeds at least hypersonic aircrafts. And also, the only way shigarakis hand/arm movement would be subsonic is if they were much slower than his movement speed which is clearly not the case as they are always showed moving alongside his body, because if they were indeed only subsonic they would be shown to be behind shigaraki as if he was doing a naruto run.