Not that I care about Bleach but fundamentally I wouldn't consider stated speed calcs as calc stacking.
If, for example, a character is stated to have a reaction time of like 1/100000th of a second, or mach 5 reactions or that they're as fast as sound, and a character moves like 20m before they could perceive them, threw a punch before they could move or intercepts them while they're running or what not or dodging them, that should be all accounts be perfectly fine.
It's effectively no different than if a character did something in a given timeframe (for example the FTL OPM calc) or like intercepting a Mach bullet, only difference is that instead of a object or the like, it's a character.
There's inherently nothing wrong with this, in fact I'd call it extremely straightforward.
Though idk if this chick actually is 100% stated to have the reactions or speed or whatever, as said I don't do Bleach, but I agree with this methodology in concept.