It can also by argued that SEO is 20% actual theory, and 80% companies arguing that they have the best methods for SEO and page ranking features. When in reality, it's 20% actual theory, and 80% advertising scam to get you to spend money with an SEO 'company' that will supposedly improve your rankings - all while trying to get your dollars.
I'm not offering any kind of SEO services to others. I create and maintain websites for my self, i promote them myself, and make half of my living from them.
I have no idea what SEO companies do.
All i know is that i can make a website to make money in a hard competition niche, using my fingers and my pc, using SEO. Not paying promotion, no nothing. So SEO does work, and it is the 90% of your website.
No matter how good is your website, it will never get TRAFFIC without SEO. And keep in mind that SEO is a two parts-thing, ON Page (website) and OFF Site. The second being most of importance.