Thank you for the info, really nice of you writing this guide.
However, I think it's pretty easy to achieve high score on clean and less complex sites. Try adding like 2-3 times more articles on your home page, similar to news websites, and see how it becomes harder.
The more images / complex website the harder it is. It would require more time and efforts to optimize everything.
Mobile optimization is mostly the hardest, and usually requires special configurations for heavily modified websites.
My point, it's not always so easy as it seems, requires a lot of testing and is very time consuming.