The article is written in a different order from stuff I've seen, but the content is pretty much a repackaged revision of what I've been reading online the past years.
What most SEO articles don't mention these days, is that many more website owners or their SEO people, are flooding the internet with the same principles. There are 10 times more websites now. If there's 300 landscape sites now rather than just 30, and if even 160 of them use some of the better strategies to fight for page one, it's still a roll of the dice.
Nobody really knows what Google or Bing has in store for changes. And it's actually pretty easy for a site in 1st position to get thrown under the bus.
So I find that as each year passes, SEO may become less reliable as a goal for generating work. 6 years ago, I would have seen the internet as the future of getting work. Now I'm realizing it's leveling-out to be just one aspect of getting or presenting services.