How complex do you think text editing _interface_ is? Cursor movement, selection, cut/paste, all that? Does MS Word / Google Docs have interface for text on the page? They do, in fact, and it’s pretty complicated thing, even if it doesn’t seem so. We’re just so used to it we take it for granted. To understand how intricate and complex text editing is, you need an app that does text editing _almost_ right, but not quite.
Meet Notion. For some reason they have not implemented text selection between paragraphs. You can’t select a piece of text from the middle of the first paragraph till the middle of the second one. Why? Who knows. My guess is it’s not that easy to implement. Fact is, take such a minor thing away and you get almost unusable text editor as a result. You can try to do it differently (which they did) or even improve how it’s done, but the end result would be: there’s nothing simpler and more natural to use than good old plain text editing.