Unfortunately, the issue is more widespread in the world of UI design. Even in closed ecosystems like Windows, you have a random mix of different UI styles, and this cancer called “flat design” makes things even worse. Carl Svensson published a nice blog post about exactly this issue a couple of years ago: https://datagubbe.se/decusab/

This reminds me of a movie from the 90s titled Mind ripper

Maybe you should try Anytype. It’s Open Source, encrypted, has applications for major OSes, provides synchronization, allows export of documents to Markdown and PDF. Sometimes it’s rough on the edges, but I think it has a potential.

Do you have any sources backing your claims regarding Kagi?