Thanks for the clarification. That is logical once you understand it.
The following points for comment:
It would be useful to include a note in the documentation on Font Book and DSGVO that clearly points out the facts.
The question is also:
Both products "Helix Template" and "Page Builder" are from Joomshaper. Why didn't Joomshaper develop the Font Book with the integration of the fonts for Helix instead of Page Builder?
My point of view
From my point of view, Font Book makes very little sense in Page Builder. Who makes a complete website with Page Builder without a template? What is the benefit of Font Book?