Whether we've seen Fuji's best or not is up for discussion; I doubt we have. I'm simply saying that his feats so far have not reached the level at which he could realistically effect light. That was the whole point of the Fire vs Lava comparison; Ace is cooler than Akainu, so his fire will cool Akainu's lava, but it wouldn't cool it down anywhere near enough.
Hang on, this is Akainu vs Cracker, Jack and Weeble. How did we get onto Kizaru vs Fujitora?