If you want to understand search engine optimization, you really have to stop listening to those in the industry looking to profit from it and simply boil it down to Google's advice. Here's a great paragraph from their Search Engine Optimization Starter Guide:
Even though this guide's title contains the words “search engine”, we'd like to say that you should base your optimization decisions first and foremost on what's best for the visitors of your site. They're the main consumers of your content and are using search engines to find your work. Focusing too hard on specific tweaks to gain ranking in the organic results of search engines may not deliver the desired results. Search engine optimization is about putting your site's best foot forward when it comes to visibility in search engines, but your ultimate consumers are your users, not search engines.
Google has solid advice in hiring your next SEO consultant, too. My advice to clients is fairly simple… utilize a platform with the tools that Google has enabled, and then build, share and promote that content through a great marketing strategy. This infographic from SEO Sherpa illustrates the strategy well.
One note on this, the infographic does warn against duplicate content. Duplicate content could be an issue if you aren't utilizing canonical links to push authority to the original article, but it's not penalized by Google.