Why SEO is so important?

SEO (or SEM) versus Social Media - which digital channel represents a bigger impact on digital activities and why?
I am an old SEO so answer can be only one. SEO. But when you go deeper you may see some additional stories told by other consultants. These stories will give you a better view on how this SEO vs Social Media duel looks like.
First of all, let me create some logic here. Comparing SEO to Social Media should mean in fact comparing organic traffic performance to organic social media performance. As such 99 of 100 times SEO will have better result. We all know that organic reach is lower every year. SEO has own challenges but hey, the intent behind the usage of search engine is way more business and conversion focus than mixed intent of usage of social media. 
Then you should compare paid search marketing with paid social media. Here social media may look a bit better. Let me est...