To clarify further when it comes to WordPress specifically, and for anyone else reading… I recommend sticking to static assets because, for example, every single page changes when an admin is logged in - a toolbar gets added to the top. Caddy might see this and cache that toolbar even on otherwise static pages.
For those individual pages, I can’t recommend enough using a plugin for WordPress itself - WP Super Cache is a standout example. A smarter cache will know what it should and shouldn’t save. You can cache the static assets at the Caddy layer, as well, for a possible boost there - but let the people who built wordpress.com figure out the more complicated caching policies for you.