I'm in the process of finishing up on a course now. The builder itself is very good. For the most part, it is straightforward to understand. The user view is also very good and intuitive for the user. It doesn't get 5 tacos for these reasons:

1. All of a sudden, on the Brave browser, text entry no longer worked. That never started working again.
2. I experience painfully slow entry times after I type my text. In other words, I click a letter, and it takes 3 or 4 seconds for the letter to show up in the text box for the lesson. I likely would have been done already if this weren't the case.
3. If you minimize the lesson you are working on, you've lost the whole lesson from your last save point. In a world where auto-save is a dime a dozen, something as content-heavy as this should have auto-save baked right into it.
4. There should be a little more for customizing the navigation, pages, etc. The ability to turn pages off, change navigation labels, etc. Also, the ability to make signing up to the community independent of the courses. We had to rework our business model because we wanted people to pay monthly for the community and then have access to the courses that interested them, but it required them to be a student in a course first.

So in summary, it could be the perfect course builder if they worked these bugs out and did a little more with the UI for course creation.