When DonWick makes threads like these I can't help but feel there is agenda involved 
My bad if it's just a honest question
Anyways, fire weakness isn't really a valid argument though, as we already know he has a pretty good counter to it.
Like has already been said, his DF is pretty lethal and has the ability to incompletely incapacitate you if he lands a hit and is even more hax than Aokiji for instance, you can break out of Aokiji's ice, or potentially break the ice if he freezes your arm but you can't really replenish your arm if Greenbull sucks the life out of it (or at the very least you can't undo that damage instantly). The man is literally a forest as well so would be a bitch to actually find and land hits on him if he doesn't want you to. His DF is fine.

My bad if it's just a honest question

Anyways, fire weakness isn't really a valid argument though, as we already know he has a pretty good counter to it.
Like has already been said, his DF is pretty lethal and has the ability to incompletely incapacitate you if he lands a hit and is even more hax than Aokiji for instance, you can break out of Aokiji's ice, or potentially break the ice if he freezes your arm but you can't really replenish your arm if Greenbull sucks the life out of it (or at the very least you can't undo that damage instantly). The man is literally a forest as well so would be a bitch to actually find and land hits on him if he doesn't want you to. His DF is fine.