Fiction doesn't have internal consistency within it's own verses half the time, creating PIS and CIS. This method is much better, considering that characters in combat should still be considered to have the same rules for reactions and difficulty with speed-- and if you wanna go that route, not only is it demonstrated that characters who are far outclassed in speed can still fight speedsters in fiction (see, Hit vs Dyspo, Gohan and Frieza vs Dyspo, etc.), But sometimes that gap in speed is just a disadvantage, not enough to blitz.
The definition of a speed gap without setting numerical standards is subjective. You could say that because she's 1.1111x faster, she blitzes him-- when in actuality, a better method of doing so is going by what we do, and checking the difference it requires to blitz us. Fiction treats speed consistently like this as well.
Another example is Lee vs Sasuke. Sasuke was able to perceive Lee's movements, but there was still a speed gap significant enough to make his offense devastating.
Here, we have clones. Lots of them. While the anime and manga have demonstrated this ability to overwhelm the characters with numbers to be iffy at times, there are plenty of examples for it, as well as explainations that can brush away the lower end instances.
Greatest examples for it are "Naruto vs Gaara, Naruto vs Pain, Naruto vs Madara's attack against the Shinobi Alliance."
Detractions: Naruto vs Sasuke on the roof and in the anime during the valley fight pre time skip. Not only did Sasuke have the Sharingan at the VoE, boosting his reactions to make it even harder to hit him, but Naruto still managed to grab him by the legs and throw him in a clone tornado against the side of a mountain. Kimimaro vs Naruto-- Kimimaro was severely superior to him in every way, including combat range, since he can just make spikes appear everywhere out of his back-- I think he actually did that, iirc. Neji vs Naruto, he managed to clock Neji when he was off guard, which would be able to be created often in a fight like this. Honestly, the stuff with the rooftop could be considered an outlier of effectiveness.
In short, characters can have a speed gap and not always blitz another character. Just like in real life. Therefore, finding the ratio of what it would take to blitz a real life person and applying it to characters, who consistently perceive their super speed movements in the same way we perceive our normal movements is the best way.
2x isn't that big. Hell, you would have to be 6x faster to be FTE, like a bullet in the perception of a normal person.
