the notion of consciousness being something an experience that other animals/humans share is entirely faith based.
the only person with evidence of ones consciousness is the person claiming they're conscious.
You're basing your premise on a lack of understanding[1], the GP's premise is based on an exact understanding[2].
You don't see the difference between your premise and the GP'S premise?
-----------------
[1] "We don't know how brains actually come up with the things they come up with, like consciousness"; IOW, we don't know what the secret ingredient is, or even if there is one.
[2] "We can mechanically do the following steps using 18th-century tech and come up with the same result as the LLM"; IOW, every ingredient in here is known to us.