That's called exhaustion. Reaction time is the brain process visual information. Chakra is not linked to that and never stated was.
if youʻre fighting against loosing consciousness and slipping into a coma, then obviously your mental reaction time will go down.
If the bodyʻs movement is powered by chakra, then obviously being exhausted to that point is going to lower your ability to physically react and respond to attacks.
Exhaustion that affects your mental state is linked to reactions. Being severely low on chakra is definitely linked to physical reactions.
Not to also mention Itachi was exhausted to death and his Chakra was almost zero, yet that didn't stop him from reacting to Kirin, which moves at the speed of light. Speed of light is faster than the brain signals. Your Chakra argument is invalid.
Itachi had enough chakra to use a susanoo powerful enough to block kirin, and then spam V4 susanoo for a couple of chapters. That in no way shape or form puts him at ʻexhausted to deathʻ and ʻchakra was almost zeroʻ before kirin hit.
lol you actually believe that lightning moves at the speed of light? Please enlighten me on how you came to this absurd conclusion.
And actually, itachi is a perfect example of this as weʻve seen that when he uses his V4 susanoo heʻs so exhausted at that point that all his body can do is slowly walk.