There is also the Navigate ▸ Open ▸ With All Subdocuments as Flat List ▸ on Editor Corkboard menu command. It has its limitations though, as it loads everything as a selection.[1] Selections cannot have new cards added, or dragged around, for obvious reasons.
But overall, I would say that if you want to work with multiple levels of outline on a regular basis, it is better to set aside the index card aesthetic, and use the View ▸ Outline view mode instead (Ctrl3 / ⌘3). The corkboard metaphor isn’t the best for this, while the indented tree view is perfect for it.
Note that if you do still want to see automatically generated synopses, while in outliner view, you will need to switch on View ▸ Outliner Options ▸ Use Fixed Row Height. You might even prefer this view mode, with that setting, for the fact that it does have a much shorter preview by design.
That said, you can effectively reduce how much of the synopsis (or preview text) that you see, by making index cards shorter,[2] so the above is not a unique ability, but it is easier to toggle a switch on and off than mess with the index card sliders.
See §6.4, Multiple Selections, in the user manual PDF. ↩︎
See §8.2.6, Corkboard Options, in the user manual PDF. ↩︎