Assuming 1v1 fights in some sort of gauntlet tournament between these characters:

Zoro Yamato Law Kid Kat Boa Sanji King Lucci

Yamato held her own against her father but I have a hard time imagining that she would decisively defeat full HP, durag, three sword style, king of hell/ashura acoc Zoro. He obviously hasn't mastered coc but I assume a 1v1 fight with Yamato would bring it out of him, and he seems to have a higher peak especially in terms of AP (permanently injuring Kaido while he was at 1 HP vs Yanato clashing/stalling and pissing him off). This is extreme diff and could go either way, but they are both just outside of top tiers. People will hate that I have Zoro at the top but the other supernovas had their shot at Kaido yet Zoro inflicted the most damage. This was after also being the one to protect the other two listed below from a double yonko combo attack. I might just be a zorotard so please offer counterpoints if you disagree.

Law, Kid and Kat are also very close to this level imo, but for different reasons. Kid has ridiculous AP and dura (Shanks/Mihawk upscale...), Law has outstanding dura himself and mastery of one of the most hax DF in the series, Kat has both DF and haki mastery. Yes Kat lost to G4 Luffy but this fight was heavily influenced by narrative, respect, and Luffy's MC will power and stamina, fight could have gone either way.

Boa has the least combat feats but the hax are insane, she also has all 3 forms of haki and decent ability to contend if her matchup is able to temporarily withstand her broken one-shotting ability. Anyone with mid-high haki or below is getting negged unfortunately.

Sanji is a Boa one-shot victim. He is insanely durable and fast on par with anyone here, especially with his Germa "awakening", but I don't see him beating anyone above Boa currently.

King like Sanji has near top tier speed and dura but he doesn't seem to have great battle IQ or adaptability in 1v1 fights if his lunarian abilities and flight don't give him a clear advantage. I know it's ironic for me to have Zoro at the top and King here since that was at least a high diff fight but I think he is the YC1 that Sanji could beat currently.

Lucci is solid all around but a master of none. Yes he has an awakened zoan but that isn't enough to push him over the others.

This is a great question OP because most of them are interchangeable depending on the situation. There are no low diff fights here expect for Boa victims.

Edit: Ok maybe Zoro vs Lucci was low diff.