The amount of different outliner programs is huge. Around 400 software projects were written in the last 30 years. The interesting situation is that most of these programs are very huge in terms of codesize. Even the minmalist cherrytree program which is available as Debian package has a footprint of 650 kb. More complex project like the Zettlr app needs around 75 MB on the harddrive.
According to the famous outliner forum, the smallest possible outliner today are Mempad (210 kb), Theguide (1 MB) and Treepad light (450 kb). Especially the treepad light software is the unofficial champion in outliners because it was created very early and was available over many years. So it seems, that even lightweight outliners have a size of around 200 kb upto 600 kb.
This codesize can't be called lightweight. Creating a 500 kb softwareproject can't be realized in a short amount of time. So the dominant question is how to reduce the code size. Is it possible to write an outliner in 10% of the treepad light size which is 45 kb and less? This is perhaps the core question for modern outliner software. What most outliners available have in common is, that they are the opposite of a small software.
It is unclear how big a project like OneNote or scrivener is, but a rough estimation is, that such projects will occupy 10 MB and more on the harddrive. It is a typical example for a typical heavyweight PC software which is created in thousands and even million of codelines.
[1] lightweight 2-pane outliner for breaking up text quickly https://www.outlinersoftware.com/topics/viewt/4707/