That's the whole point. The sky is blue is trivially observable. Any claim that someone has disproven something that is trivially observable should be met with skepticism.

If you have something that needs to be done, and an agent goes and does the whole thing for you without mistakes, it is trivially observable that that is useful. That is the definition of usefulness.

But useful in the context of these debates isn't that it solves any single problem for someone. Nobody is arguing that LLM's have zero utility. So I don't really see what your point is?