We can't even decide how much, and of what, would constitute a person. If like you said, the best AI right now is just a portion of the language processing part of our brain, it still can be sentient.
Not that I think LLMs are anything close to people or AGI. But the fact is that we can't concretely and absolutely refute AI sentience based on our current knowledge. The technology deserves respect and deep thoughts instead of dismissing it as "glorified autocomplete". Nature needed billions of years to go from inert chemicals to sentience. We went from vacuum tubes to something resembling it in less than a century. Where can it go in the next century?