CDN is only for static content and I was assumed all your static content would be already on a CDN... it's a standard practice.

CDN is NOT only for static content. Minimally Cacheable, or catchable based on cookie value, content can be cached on a CDN. Also running ALL traffic through a CDN (like CloudFlare or Akamai) allows you to do traffic optimization, FEO, DDOS protection, and much more.