A "Mental Nerf" Is No Excuse for Kizaru Failing to Deal Significant Damage
Even if Kizaru is the one who gave Luffy food, it doesn't change the fact that he did a 1/5 star performance against Luffy.
He only did the following:
1. Kicked Luffy through a robot
2. Scratched Luffy's cheek with his light sword
3. Accidentally hit Luffy with a laser he intended for Vegapunk
Even with a "mental nerf" he should have been able to do more than that.