This is a bit like going back in time to the beginning of the industrial revolution and estimating the impact of a mechanisation based on comparing the speed of early mechanical looms vs. a skilled human.

It takes years or decades for the automation of an artisan process to shake out, because it involves rethinking how everything around the now-automated process happens, and because the benefits involve the automation's ability to continue scaling beyond a level where human capacity was saturated. We're only at the very beginning of that process for coding, and right now we tend to see LLMs somewhat awkwardly inserted into pre-existing software development lifecycles. But it's unlikely that'll be still be the way we're creating software in 10/20 years time.

Except that LLMs are only being trained to do things that humans can do, not things that humans cannot do.

I have heard a lot of claims like this, where we cannot imagine the benefits of AI because the work will look so different to how it is now, but I have yet to see that actually demonstrated anywhere.