Difficulty scores are the SEO market's answer to the patchwork state of all the data out there. All five tools we tested stood out because they do offer some version of a difficulty metric, or one holistic 1-100 score of how difficult it would be for your page to rank organically (without paying Google) on a particular keyword. Difficulty scores are inherently subjective, and each tool calculates it uniquely. In general, it incorporates PA, DA, and other factors, including search volume on the keyword, how heavily paid search ads are influencing the results, and how the strong the competition is in each spot on the current search results page.
The audit is for all pages and not only one. What happens in the majority of the cases is that pages / posts have similarities so you can group them together. For example the pages of a website may be ok but the blog post pages may be missing titles. It’s a lot of work especially for a 500 pages website but you can start from the most important pages first and work your way to the rest