But Ace also lived in the New World and for 2 years iirc before being under WB's protection. It was said Logia who are overconfident in their fruit die in the NW. Plus the fact that Logia's intangibility is a subconscious act, a Logia will become intangible when attacked even if asleep. This means Logia can't make there body physical at attack yet Ace's body stopped Akainu's punch, if he can't make his body solid then the only way left to stop it would be haki.
Key word is overconfident. Who says Ace was overconfident with his fruit?
The bolded is just completely wrong.
1. Logia eaters can keep their bodies solid if they want to. The subconscious transformation occurs after training and mastery of the fruit. If a Logia just became intangible whenever something hit them, then a Logia would never be able to touch anything or be touched by anyone, even a hug or handshake, without bursting into the form of their element.
2. Akainu's magma neutralizes Ace's Devil Fruit. When Akainu shot magma at Ace, it burned his physical hand and stopped it from transforming.
3. Ace jumped in front of Akainu's fruit to protect Luffy. What damn sense would it make for him to disperse into flames if he's trying to act as a shield?