I routinely do articles that are 750-1,500 words using Obsidian, and I would have no hesitation going longer. I write the whole thing in one document. Sometimes I use headers to break things up but that’s mainly for visual highlighting as I scroll down.
I d not go in for zettelkasten or atomic notes. I wrote long notes, hundreds of words each.
I’ve been a professional writer and journalist—which is to say, a professional note-taker—for many, many years, and have evolved my own ways of doing things. I gave zettelkasten a good hard try 2020-22 or so and it just does not work for me. Although I realize that I do something zettelkasten-like just using cut-and-paste with the clipboard.
I started a topic recently here about my favorite Obsidian plugins. Almost all of them relate to writing.