What problem does this address?

Currently users that do not have the edit_theme_options capability can not create a navigation block within the contents of a psot / page. This is because, they are unable to make a wp_navigation post and save it. However, using legacy menu / menu items, they should be able to import them and create a navigation.

What is your proposed solution?

Instead of saving navigation post, save the block data to the content of the current post or page.