WordPress a PMS (post management system). It basically have one type of content, a post. Even a page in WordPress is really post. Over time WordPress has gotten really good at managing posts. It's now to the point where a post can be virtually indistinguishable as a post. So it appears to be a CMS. However the use of a post as the base level of content type leave big holes in the system. For example you can't like to another page within a post as piece of content. It's linked as a url and if the page moves the link is broken. Many such holes exist, but for most projects this is not a problem.
I've always considered WP to be a CMS, but switched to a wiki as my primary CMS primarily because I wanted a complete edit history. But one thing I like about the wiki is that links to other pieces of content are links to the content, as opposed to WP's fragile URL-of-the-moment. I never thought about that issue in the WP context before, but this is a spot-on critique.
OtherMichael