[dangerface]

(registering custom post types, adding & customizing options pages, removing unnecessary tabs per user role, etc)

Thats my point you don't need to do any of that with a CMS it just works out of the box. People may be familiar with the admin interface but that doesn't mean its good, just that they havent seen anything better, if the admin interface is as good as something like perch you wont have to train the clients (we do anyway) its all just intuitive.

I cant reply to your other comment but I do still have to work with wordpress and I also use ACF Pro, it sucks so many plugins made by third party developers who have went bust and left me to maintain their garbage code.

As for alternatives I use and recomend https://grabaperch.com/