For me its an L if characters like shanks , admirals or even gorosei prove themselves to be above Kaido. The more characters show themselves to be above him , the bigger the L is for Kaido as a whole.
Here I will say admirals? Given they hate Kaido the most here and are most anti Kaido. Take Lee hung who makes 3-4 anti Kaido threads a month.
I think it's more than strength, really...like take Dragon, in a way Kuma sort of ruined his agenda with the flashback where he didn't save Ginny lol. It made him look bad.
Or Sengoku who gets shit for his performance versus BB and Co at MF despite being stronger than them.
Or Vista and Franky being used to downplay Mihawk and BM.
For example, Imu is probably gonna surpass WB but no one's going to regard WB any less for it unless Imu makes him seem less cool overall.
But meanwhile WB not trying to rescue Oden the way he did Ace is sometimes used to downplay him and the MF top tiers by comparison.
It's just how these fanbases work nowadays, with all their talk of "aura" and such. They don't really care for context so much as a character's perceived image.
Ig for Kaido, yeah, you're right - anyone who makes him look weaker is a threat. For this forum I suppose it's the Admirals - most Zoro fans I see here like Kaido, so he's not gonna get hate from them.