I think the point of the comment isn't to have this finishing layer to make things "better", but to make things "legal".

Humans are allowed to synthesize a bunch of inputs together and produce a new novel copyrighted.

An algorithm, if it mixes a bunch of copyrighted things together by itself, plausibly is incapable of producing a novel copyright, and instead inherits the old copyright.

Just like Clean Room Design (https://en.wikipedia.org/wiki/Clean-room_design) can be used to re-create the same software free of the original copyright, I think the parent is arguing that a mechanical turk process could allow AI to produce the same output free of the original copyright.