How do I make my site with pre-loaded content and pre-loaded config available to others without creating a distribution?
One of the support staff at MoreThanThemes was kind enough to provide some direction on how they do this. You can see the result in the structure of their free or paid themes. In short, the steps are pretty simple for what might be termed a cloned installation. The steps are basically the following. 


Create a clone of the site that you want to install (https://www.youtube.com/watch?v=9NMRwkTzrCM describes that pretty well)    
In the clone, overwrite/replace the /docroot/default/settings.php file with the docroot/default/default.settings.php file
Make a clone of the original database (e.g., using MySQLDump, PhpMyAdmin copy or drush sql-dump) and install it in a new database instance that you will use for the cloned site.


If you also have removed the Umami distribution and the minimal distribution from core, then the installation wizard will automatically bypass the choice for which install profile to use. In that case, the installation wizard only asks for the database information, where you will use the information for the cloned database. That will be all you need, and you will have a installed clone of your original website. 

From my testing, it looks like the UUID of both sites are the same, just as if you had cloned the original site. So, the main use case from what I can see for this scenario would be if you wanted to share a copy of your site with other people, including the content (like the theme companies do). The only difference from a regular distribution like Umami or OpenAtrium from the user's standpoint is that they have to load the database file on their own before they do the installation. But from a developer's standpoint, this seems to be a much easier approach to sharing a website with the content and should be adequate for many users who want to test out your site. 

I am surprised that this is not more widely documented and perhaps I have missed something here. But in my tests so far, this seems to be all that is needed. Hopefully this will help someone else who may need this simpler approach.