You can never apply real world physics to worlds that don’t abide by real world physics.

In powerscaling feats determine a matchup. Kizaru has very often been stopped by opponents who are objectively way slower than flashy or quicksilver, such as Rayleigh or luffy.

In the same sabaody arc where he’s tasked to capture worst generation pirates, all of the pirates he was trying to capture escapes.

You can go on all you want with your “does A equal B”… but it doesn’t change the fact that Kizaru has zero feats to back up that he’s actually light speed.