Since we're at the topic of Byakugan, I'd like to bring up another theory about Byakugan being able to keep up with an enemy who uses swift release.
The swift release jutsu, that enables the user to move in a faster pace:
(Hayatōn: Mueishō) – Swift Release: Shadowless Flight
Rank: A
Type: Offensive, Defensive, Supplementary
Range: Short
Chakra cost: 30
Damage points: 60
Description: After making a single hand seal the user can move at fast speeds through the release of the swift release and then strike their opponent at multiple angles. The jutsu is effective against strength based close-combat Taijutsu users such as Tsunade and Sakura.
However sharingan of tomo 3 is capable of reading the movements and can react to the opponents attacks.
Note: Can only be used by a swift user bio.
What I had just bolded there is saying that a 3 tomoe sharingan is capable of reading the swift movements. We got that down.
Let's look at the "What speed level peoples eyes can follow"
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For the sharingan, it is:
-3 tomoe: x2
For byakugan, it is:
-Byakugan: x2
My point being is that since both eyes possesses the same speed levels, byakugan is able to read an enemies' movements, who uses swift.
Am I wrong, somewhat wrong?