SEO is not about backlinks.
Backlinks is an aspect of SEO. SEM / SEP has nothing to do with backlinks.
In it’s basic format… SEO is about getting organic traffic. SEM / SEP is about getting paid traffic.
With SEO… you don’t know what you get… but it’s free. Your cost goes into producing quality content.
With SEM… you get exactly what you asked for. And you pay through the nose for it. Your cost goes into paying people to develop your landing pages, and managing / displaying the ads.
We do SEO and SEM. Some of our clients pay only for SEO… some only for SEM… some BOTH.