its better to have a cms to have highly optimized seo site. Why?? They have seperate plugins that does all the work which you do manually in non cms sites.
Most CMS are SEO Friendly so any noob has On Site SEO easy made ... and they only have to handle off site (backlinks)
It needs CMS that allows non-technical users to easily specify keyword rich URLs, title tags, descriptions and image alt text.
It depends on what CMS you pick. Not all CMS are very search engine friendly and not all offers seo plugins etc. Do your research before choosing CMS