Reasonable people can disagree and my phrasing was probably a bit over-seasoned, but neither side has a rigorous proof regarding AI or human intelligence.

If nobody understands how an LLM is able to achieve it's current level of intelligence, how is anyone so sure that this intelligence is definitely going to increase exponentially until it's better than a human?

There are real existential threats that we know are definitely going to happen one day (meteor, supervolcano, etc), and I believe that treating AGI like it is the same class of "not if; but when" is categorically wrong, furthermore, I think that many of the people leading the effort to frame it this way are doing so out of self-interest, rather than public concern.