Existing multisite import existing standalone as subdirectory

I know I’m committing some kind of holy treason but someone was bound to try this for the sheer fact that it’s possible so here I am with at least a motive. This also includes DIVI. I’m just posting this for others who are crazy enough to try it but mainly for advice because I’m not 100% understanding a part of this and it’s slightly bothering me.

Motive/Project: Rebrand a standalone as part of our main marketing site.
Constraints: Time-sensitive, least-cost plan, no sub-domains, no re-entry of data, only one db per site instance (host limitation), separate themes (js_composer vs. divi theme), separate plugins

Pros of Multisite:

• One database
• Separate activated plugins/themes
• Faster implementation than manual re-entry
• Sub-directories supported

Cons of Multisite:

• Not meant to use sub-directories on existing sites
• Some settings may not carry over
• I learned DIVI does not play nice while importing options
• Large import files (use wp import) can stall midway due to the nuances of your plugin environment compounding issues
• Menus not syncing up and duplicating when you have to restart the import

Here’s the overview of what happened.
Order of operations

1. Backup the staging area of test env
2. Enable multisite for sharpspring.com
3. Update Nginx server for multisite compatibility
4. Add a new site to the network: Network Site B
5. Backup the staging area of test env
6. Add plugins and theme from Old Site B redesign site instance
7. Add users to the new site. Any others from the import should be re-created
8. Import Theme Options, Theme Customizer, Theme Builder, and Role Options for Divi
9. Add license keys and usernames for Divi products
10. Import All Content from Old Site B site into Network Site B with WordPress Importer
11. Update Settings > Reading to set the Homepage

The issues were mostly laid out in the Cons section but again I wasn’t seeing DIVI options carried over correctly and presets were flat out missing. I also noticed the import failed and timed out in the GUI so I recommend trying it out in the command line (ssh into dest server and use wp import). At least there you can restart it partially from where it stopped (or it detects what already exists). Although this happened twice during that step so menu items were duplicated. A pain but easy to fix.

Divi things not carrying over
Theme Options
Theme Buider
Theme Customizer

Things I initially tried to fix that

• rename et_cache and resave Options
• Disable all firewall plugins, wp-rocket, and other could based plugins (amazon web services)
• Clear browser cookies and site data
• Clear cache using hosting provider-provided tools

After trying the above and losing sleep over it, I finally settled on the idea that something in the import was not syncing and it was probably due to there being existing content on the main site, Network Site A.

Again just wanting some confirmation on this, maybe sharing some experiences with other forum users, and a little of “You should have known better” ??

Host: Kinsta
Server: Nginx (host enabled multisite server requirements ahead of all this)
WP: 5.5.3 and soon to be 5.7 after another long journey with jQuery migrate.
PHP: 7.3
Site A: WpBakery+WP-All-In-One Firewall,Redirection,