Exactly 8 pages of quality content is what gets a band 6. any less is a 5 or less
No, NESA doesn't specify that therefore the claims are not true. If you look at student samples on the NESA website, a band 6 response for 3 modules each was 5 pages. You simply can not say a certain amount of pages is insufficient.
When HSC markers receive marking guidelines, it doesn't say "make sure the student's response is above 8 pages to give them a band 6". Also, have a look at the marking guidelines under "In better responses, students were able to", it doesn't say, write more pages, rather things like "consider all aspects of the question in their response". Under "Areas for students to improve", again it doesn't say "write more pages" but rather "analysing rather than describing texts"
Getting a good band is about impressing the marker with what you know,
not how much you can write. And listen, it's really not good to keep on thinking that pages equate to certain marks/bands. It's all about knowing your content, so make sure you know your stuff and then just put it down on paper. We've emphasised this so much man, come on. Hope this can change your insight.