Look….
JJK has a somewhat consistent speed increase so long as you remember the author is absolutely awful at any type of speed scaling pas sub-hypersonic ranges.
Piercing blood is considered fast at Mach 1
Cursed Naoya, who was previously having trouble against Choso as a human, gets an increase to Mach 3 which is seen as incredibly fast by top tiers in the verse.
Gojo’s 200% hollow purple went at a little over Mach 10 when he fired it based on the real life distances Gege both used and mentions. This makes sense because Gojo is seen as the pinnacle of the verse and his attack is sizably above Naoya’s Mach 3 type speed which he needed to become a cursed spirit to even be able to perform.
This is all a relatively consistent chain of becoming faster the stronger the characters are.
The cases in which we get massively hypersonic stuff are pretty big outliers that are based on very minute feats, along with the general inconsistency the author has shown in regards to how fast the attack he’s putting in moves and what that means for the character in question who dodged said moves.
Like for example, one of the more egregious examples which happened very recently mind you was Sukuna getting tagged by SONIC WAVES yet somehow, at the same time being perfectly capable of dodging ELECTROMAGNETIC WAVES at point blank range, while extremely injured no less too.
Outside of the sheer and mind boggling inconstancy there is from the fact that Sukuna was somehow tagged at something that moved at the speed of sound but dodged something that moved at the speed of light the very next page after, the very fact that Sukuna is able to perform what is by en large, the best speed feat in the entire series by orders of magnitude, while being critically injured no less, suggests to me that the author didn’t understand the nature of the move he’s detailing, leading to incredibly high yielding results that are not intended to be interpreted with how the general narrative has portrayed the characters’ speeds in question.
That’s my two cents on the matter, take it how you will.