Maybe I am missing something. But in a large page, when you click outside the content and the CMD-UP a few time all blocks are folded till the main level, effectively the H1 level.
When I CMD-DOWN 1 time it opens the H1/H2 level.
And sometimes I even go further down but most of the time from this level I enter a Block by hitting the bullet and I can edit (also the sub-bullets for that H3 level).
And using the breadcrumbs at the top of the page I can quickly see where I am and navigate to a higher level … to deep dive in another place in the document.
So I guess an outline overview is already in the document.