I propose an experiment where a fat man sits on a fire to settle this question
Finding a fat man wouldn't be hard, but an intelligent fire than can move around as it likes could be a problem.
–- Update From New Post Merge ---
Unless he can control it in the "dark-hole" level, not even lighting can escape from those galactic buttholes.
Dark hole attracts matter towards it and absorbs it, Fuji's gravity just increases weight in a set area. There should be a clear an obvious difference right there. Fire has a lot less weight than solid matter.
Don't tell me you think that logias whose elements aren't solid matter wouldn't have more chance against Fujitora than normal people.