I'm leapfrogging over Dynalist and InfoQube, since you've already decided they won't work for you. An outlining app that is now defunct, but which might still work is called Noteliner. It is very clever. You can download it here:

https://download.cnet.com/Noteliner/3000-2076_4-75328353.html

Here's the webarchive of the original home page:

https://web.archive.org/web/20151110020459/http://www.noteliner.org/i/Main.html

From your description of how you use ECCO, perhaps an app like Scrivener -- incorporates an outliner, but really isn't one -- would work:

https://www.literatureandlatte.com/scrivener/overview

Steve