Yes we want to collect data from these users buy we also want them to ‘learn’ what they’re being onboarded to. It doesn’t make sense that they can’t see the public facing website (where the URL becomes the onboarding form). Or that they can’t read the Terms and Conditions from the onboarding page (where the url changed to onboarding form).
These are pages we choose to be visible to everyone so therefore they should still be visible to everyone. I agree they should never be allowed to log in without the onboarding form complete. Pages visible to everyone are for non logged in users. It would not matter giving visibility to these pages visible to everyone before or during onboarding.