As you noticed some Kid fans are complaining about not only Shanks's Kamusari did one-shot him its because Damned Punk exploded on Kid's face and the combined damaged KOed Kid.
Its fair, however, I think Oda did this on purpose because the reason why Law + Kid won vs. Big mom and the result of that they earned 3 billion each and earned the right to challenge Yonko because Big mom suffered the same bad luck on Wano before losing:
Big mom didn't know that was a bomb same as Kid didn't know Shanks could move that fast from that distance and can make Kid's own weapon explode on his face while sending Kamusari.
Ironic Yonko revenge by Oda, and it looks like Oda did it on purpose.
Its fair, however, I think Oda did this on purpose because the reason why Law + Kid won vs. Big mom and the result of that they earned 3 billion each and earned the right to challenge Yonko because Big mom suffered the same bad luck on Wano before losing:
Big mom didn't know that was a bomb same as Kid didn't know Shanks could move that fast from that distance and can make Kid's own weapon explode on his face while sending Kamusari.
Ironic Yonko revenge by Oda, and it looks like Oda did it on purpose.