What feats chicken king have to suggest that he high diffs Prime Garp when he himself always said that he and Garp always nearly killed each other?
This was just Oda giving Shiki some respect because he doesn't like top tiers losing in straight 1 vs 1. Even Kaido and his bet on him in 1 vs 1 doesn't have any clean win against a top tier.
Marco was able to stall King and Queen for a while despite many seeing him as inferior to King
In the end Garp was completely scratchless post-fight while Shiki was bathing in his blood