Surely you don't. If its 20 chapters where its Luffy vs Kaido 1 V 1 and 2 chapters where it isn't, you'd say it wasn't 1 vs 1 because you are biased.
No
it's the fact that Kaido has fought 17 people alongisde Luffy before this stage of the fight without taking breaks, like Luffy did
and while also fighting all these people and Luffy, Kaido was also holding and moving an entire island
for me to consider something a full fair 1v1, both characters had to go at it with full health and power from the start, without interference from the outside and without the fighters having any type of nerfs
and to me using stuff like "Luffy was also nerfed" for example, doesn't really work, because you simply can't compare and equate the things that happened to the two fighters to determine if it's fair and stuff
even if Luffy is way more nerfed than Kaido for example, it already makes the 1v1 scenario weird, because they aren't both at their max for us readers to judge