But are these actually completely different technologies, and if so, where is the dividing line? Firearms certainly have not decreased in significance, and they're the modern version of a bow, which is simply 2 iterations later in propulsion methods: tensioned string -> high-tension cable -> high-pressure gas.

Are LLMs really going to fall off in significance, or will it just be the nth newest incarnation of LLMs?

The function of what an LLM does (generative language) is what people seem to take issue with, but the function is here to stay, even if the next iteration has a different name or method.