Looks like Ace could have wiped out half of the island by setting the big blob on fire. I wonder why Caeser told the thing is weak against water. There's plenty of water around, so why would he tell the people how to fight it?
Luffy made a bad call by hugging the madman instead of knocking him out. Caesar doesn't really strike me as an awesome fighter, but the fruit ability is highly dangerous.
Oh, sorry. I guess I read too much into it, when you started to list strong people with different abilities. I only mentioned the dead man because he was a fire user, not really because I'd have thought only really strong people with specific abilities would stand a chance.
Still, I'm confused how, if fire makes it explode, it wasn't constantly exploding when it was rolling over the firelands.
Maybe because it was moving all the time. It might be covered by some slime that offers limited protection from fire. The flamethrower took quite a while do anything. A normal animal would have died in a fraction of the time.