That's true. It really depends what kind of queries someone wants to run. Even in current example, you could end up joining same table multiple times to get a desired result and graphs would do better than a relational database.
Actually the document model fits more cuz we don't actually need to traverse but to compose everything into one UI.
As in the pic, we show all the track workshops on the right side, and we calculate the percentage of the shown lessons of each workshop, so we need to get everything of each workshop at once.
But for the profile we have a similar case, each profile has dozens of tasks, quizze, and projects... and we will traverse them on demand (lazy-loaded).
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