Eh, I've heard that theory before, I'm sure we had alot more than three predators to blend together. Nevermind how that forgets about fire-breathing or the varying descriptions of dragon species.
Like dinosaurs effecting the fear response, and also how fire was in nature such as forest fires, or primitive ideas of fire when it was first becoming developed.
Yes, but fire is a rare element in nature, though admittedly so is it in dragons. Most tend to have poison, frost-breath or even as rainbringers in eastern mythology.