WordPress as CMS
I don’t think you will find any two people who agree completely on what features are needed to have a ‘real’ CMS. I have my own views on the subject, but I think I am swimming against the tide. Anyway, here are my thoughts and a couple of tutorials that explain how others use WP as a CMS.
FWIW, it seems to me that a full CMS needs to allow the definition, storage and management of specified types of data: text, dates, numbers, images, etc, with rules about the acceptability of content and relationships among the different instances.
WP allows mainly storage of undifferentiated blobs of text, with little control over the content and relationships. (Although you can provide some of the facilities with various plugins.)
I would also add that, in my experience, WP is sorely lacking in built-in search capability. I don’t know of an easy ad hoc way to say: show me all posts with A and B, but not C or D.
Ditto for reporting, importing, and exporting.
Now, I will say that a lot of this can be overcome with plugins or custom programming, if you are willing to put in the work.
Just my opinion.
Here are the tutorials: