It's true Fujitora's ability doesn't work so well against fluid bodies, but you know GB is a bit different than the rest of the logias. Gravity hard counters his ability, and he could probably crush the whole battle filed and turn GB into fire wood, and deflect any tree branch coming his way too easily. Not to mention the meteors and explosions. GB is everything you say he is, but it's just that Fujitora is a bad choice of opponent for him. If it's revealed that Fujitora can imbue his gravity with Haki, then the man's fucked. Even the other logias will be endangered by him if that happens. Fujitora also has these future FA vibes around him.
I don't know if he's not serious, but he definitely knows he's wrong but still decides to post those shitty takes to one up Zoro bros and me.