Powers & Abilities IJ is hottest flame in One piece and Oda already told us

[Egghead]

These are facts. No flame shall ever compare to sanji ever again. I won't be surprised if he gets black flames and no one else ever reaches blue flames like him

Sanji the maverick. He's gonna do what no one else has ever done. Just like finding the all blue

Spittin

 

[EmetSelch]

Sanji has the hottest fire yet it can only burn his opponents at the most, not like kizaru laser, akainu magma or kaido fire that literaly melt things

 

[PurpleSwordsman]

Mera flames are considered "real" flames
It should be better by logic.

But yes, he burns more than real flames. Nothing wrong with it. It's fiction and he is a superhuman with superhuman feats.