Isn't it consensus that EL powerups all came out of nowhere?
Using the flames on his swords isn't really "he can cut fire now".
The foreshadowing of a "fire cutting technique" came with Kinemon.
Not only that, unless you have some kind of magical sword, setting the blade on fire actually takes a toll on it and will deteriorate it faster, making it good for one time use, but trash on the long run. Looks pretty, but it's bad AF.
Or are Zoro's swords.........
....
MAGICAL SPECIAL SWORDS LIKE ENMA???
:D
If he used Enma to cut the fireball, i'm gonna laugh. Ngl.