I miss spoke when I used the word “page”, as I would like for my users to create a website within my site with several pages within the theme that they purchase. Again, maybe I’m using the wrong words as I am new to WP.
For example: https://www.weddingwire.ca/wedding-websites
On this site, users can chose a theme/website and have several pages regarding their wedding details.
When you said “Whereas in multisite, users really could select from a limited set of complete, readily available themes.”… this is exactly what I want.