Gosh. You are greatly overcomplicating things.
First, this is totally wrong:
This shows your CMS with a Rich Text field that has HTML copy / pasted into it.
You can’t do that. That’s why it’s spitting out HTML tags on your published site.
If you want to add raw HTML into a CMS Rich Text field you must do so through the API.
That’s how you win.
Second…
Stop with all of this Embed elements within Collection Lists, within Rich Text fields stuff.
Take a step back, breath deeply and simplify 
Step 1:
Send simple, raw HTML into a CMS Collections Rich Text Field via the Webflow API.
Something like:
<h1>Hello</h1><p>This is some raw HTML.</p><p>Did it work?</p>
You can use the API here: Create Collection Item
Step 2:
View it within the CMS field. Notice how there are no raw HTML tags. Instead, an H1 tag is rendered HTML. This is correct.
Step 3:
Display this in a CMS Collection Template (skip the Collection List element for a moment, simplify).
Did it work? It should have.
Step 4:
Try again in your Collection List element.
You should have success with this approach 