what exactly are the reasons for Kira winning? Isn't a punch faster than Kira writing even if Saitama doesn't attack instantly?
Not at all, Light can easily right his name before the shockwaves hits him.
I don't understand the issue here, you made their speed equal. He can react to it just fine.
Speed Equal means watching someone who's equal to you, run a distance of 50 meters. For average humans, such a distance would take 8 seconds. Since Light is equal to Saitama in speed, the average punch speed of a boxer is 11.5 m/s, which is a timeframe of around 4.3 seconds. Should be enough time to write down his name.
The shockwave of a punch would travel slower than the actual punch itself, but not by a large amount in fiction. Also even though I say four seconds, I don't actually mean four seconds, but what Saitama and Light would perceive as four seconds.
This is still inconclusive, since Light will die from Saitama's attack and Saitama will die 40 seconds later. Light can't write faster than Saitama can throw a punch, and he can't stop his shockwave attack even if he kills him instantly. Though I don't think he'll have anytime to write anything other than Saitama's name.
Speed Equalization rules: "The combat speed of that faster character is assumed to be equalized to the combat speed of the slower character.
Every other speed the faster character has is reduced by the same multiplier. This includes the speed of any attacks, projectiles, reactions, perception, flight etc."
Saitama's attack speed is reduced as well in this situation. Since all of Saitama's speed values are equal to each other, there will be no difference in their speed, the speeds of Saitama's attacks can be reacted to by Light in this situation. This would only changes if Saitama's combat speed was slower than his attack speed.
