I am not arguing Luffy isn't temporally down as well.
What I am saying is just manga facts this was Luffy when he punched Kizaru
Again Luffy is down due to himself and not a Kizaru attack, the guy was literally CLEAN before hitting Kizaru.
Kizaru being down AFTER ONE HIT, is a bad look for him no matter how you try to spin it. Kizaru is also the first character to go on cooldown along with Luffy when his Gears expired.
Luffy being down due to timelimit of a ability of his =/= Kizaru being down after being punched a single time.
Is it that hard to understand?
It doesn't matter if both are down, Luffy will get back up and will be able to use his ability all over again. If a single hit made Kizaru lose his legs and be unable to move, any Gatling technique is doing the trick next time.
Kizaru's hack (light speed) is what is keeping him on this fight, and that's fair. But it won't last long anyway.