Yes, LLMs are currently useful and are improving rapidly so they are likely to become even more useful in the future. I think inevitable is a pretty strong word but barring government intervention or geopolitical turmoil I don't see signs of LLM progress stopping.

Why would they progress significantly than where they are now? An LLM is an LLM. More tokens doesn't mean better capabilities, in fact, quite the opposite seems to be the case, and suggests smaller models aimed at specific tasks are the "future" of it.