I would argue that SEO is really a more all-encompassing term that would include Social Media under it's umbrella. I wouldn't consider them entirely different entities. Conversations occurring on social media platforms are very much like conversations occurring on blogs and forums in many regards. Social media sites just have a bit more of a walled garden and a tighter knit community around them.
Personally, I think social media on it's own is starting to lose steam. There was a rush of people calling them "social media experts" a few years ago, as if it was some sort of new profession, but people are starting to wake up and realize that is ridiculous and many of the things that need to be done to promote and market on social media are already skills that folks working in marketing already have. I would trust a more seasoned marketer with my social media accounts, than some person with no professional work experience who simply plays around on Facebook and Twitter all day.
The other thing to keep in mind, is sites like Facebook which dominate social media overall are quickly losing popularity with the young crowd at a very fast rate. They are growing tired of being "monitored" by their parents on there, and are instead flocking to other networks such as Tumblr. In addition, Facebook has made some big mistakes with regards to how it is limiting posts, and making people pay for their posts to be seen. This is causing an overall decrease in quality content on there as more advertisers are treating their paid posts as ads rather than conversations. Either that, or they are posting a lot of mindless click bait to try and improve their scores.
I think a broader more long term focused SEO strategy is far more important than putting all of your eggs in the Social Media basket. Many of the tactics people are using to gain quick wins on social media sites are not sustainable and are more or less the equivalent of black hat SEO.
