In terms of development, I love Joomla, because it is so easy to develop modules or plugins, and also to integrate a custom HTML into it! (Joomla uses a standard called MCV (model controller view), this allows the customization of the "design" without interfering with the code! (Wordpress doesn't).
The template chosen won't interfere with the back-office (Wordpress has that problem).
It allows the override of the template (customizations) or extensions (modules, etc), and won't be destroyed in case of an update to Joomla.
Also, Joomla can be used as a platform and build applications on top of it, using its API, etc.
In terms of "ready made", it is also very good, version 4 alows the customization of the back-office with a lot of options and there are a lot of free templates (and some really nice ones that are payed, or downloaded here...).
There are also a lot of editors available, this allows you to create an almost seamless edition (also there are extensions that allow you to edit in the front end, see SP Page Builder).
The main "selling" point for me, is that there is no need for extra plugins/extensions to perform the basic functionalities (SEO, multi-language, etc), whereas for instance Wordpress needs a lot of plugins...
Joomla is realy fast, especially version 4 in PHP 8.1!
I have been using it for the last 16 years, so I could go on and on with more benefits.