Fair enough. It just seems to me that since they have firebenders, they already have (in some form) the idea of explosive weaponry, which the Chinese did not necessarily have. I'd think that would tend to accelerate the development of rockets and cannons... except, of course, for the social/spiritual stigma against diluting the power of firebending. The two factors probably balance themselves out, to some degree.

So it's reasonable for the Fire Nation not to have invented guns yet. But that will not last forever. (It might be especially messy if the Earth Kingdom invents them first.)