1. Superflare is not a threat. Kaidou
can see several seconds into the future and he has the
ability to release his own omnidirectional shockwave with over 2x the AP of the Superflare. That would stop the heat from ever reaching him.
2. Kaidou is far faster. Speed is equalized to base, meaning that at his peak Kaidou would be 12x faster than Superman, which he can
increase even further with blitz attacks and
higher variants. Kaidou can see the future so no attack is getting to him.
3. Kaidou also has Advanced Busōshoku Haki which
makes a barrier of emitted Haki, which has
proven to be able to block heat. Unless Superman has higher AP than Kaidou's Buso Emission (he doesn't as Kaidou has the 2x advantage), no heat from Superflare is getting through, it's just getting deflected by its attack reflection.
4. Kaidou can create
several tens of kilometers of Flame Clouds that are big enough and dense enough to rip up an entire island from bedrock and carry it across the skies for several hours. They have higher durability than the AP of a Superflare, and Kaidou
has been shown to be able to coat his entire body in this. He would not effected in this case, as they could cushion the drop of an island from hundreds of kilometers in the air.
Kaidou also severely upscales from his 24 ZT value. Luffy, who was already > the 24 ZT due to statements and was fully incapable of doing anything to this version of Kaidou. Each one of his attacks nearly KO'd him before he even went all out. In his bulked form, which he can spam, Kaidou becomes
much stronger (in value he far upscales over 2x). Luffy at his strongest couldn't even hurt Kaidou and this is after Luffy's passive stat amp. Kaidou would break through Luffy's layered defenses and completely stonewall him until he used his final attack or dura neg (although the latter didn't do much).
I'll leave my vote for Kaidou.
