Yeah, they both have DBs, and you can kind of outline inside pages. The difference is that, technically, in a "real outliner", each "node" (or line) is (by default) a different entry in the database, whereas in page-based apps (Capacities/Notion), it is the whole page.

Capacities is partially going in this direction. Notion, less so, but it is simple and advanced (linked records...) and hence a favorite of mine too.