I'm not even talking about Ifrit Jambe. Sanji's base heat resistance and heat with Diable Jambe is much hotter than Ace. It just simply has a way better scaling chain.
Akainu Ambient Heat < Base PTS Luffy < FMI Haki Luffy Heat Res ~ Jinbe Haki Heat Res < Promentheus Heat < WCI Luffy Heat Res < WCI Sanji Diable Heat <<< Sanji Ifrit Heat
Akainu Ambient Heat >= Ace Heat
Sanji's armament haki feats include:
- Blocking a point black blade strike from Daifuku
- Blocking a spear attack from Judge
- Protecting himself from Ifrit heat which automatically puts him above Ace's due to him having near 0 feats of Armament
Sure, Ace was able to fight with someone equal to him in power for 5 days, but Sanji literally said that having
all of his bones broke + having his organs damaged beyond repair stung
A BIT.
Ace can do NOTHING on the level of that to Sanji, therefore Ace won't be able to put him down.
Also, what's stopping Sanji's flames from just engulfing Ace's fire with his own?