For me one of the biggest issues with Notion (and to a smaller extent with Obsidian as well) is its ever present UI. When I write (or read) something, I don't want to see 20+ buttons scattered around distracting me from the content.
IA writer got this right, but it's too local and doesn't have colab or better online sync features. Shameless plug – I'm building https://kraa.io/about that's trying to be a writing app with a minimal, yet feature-rich, UI. (better offline and local-files functionality planned)
You want a focus mode plugin:
https://github.com/ryanpcmcquen/obsidian-focus-mode
This is what differentiates Obsidian from many other note taking apps. Anyone who has an itch can build a plugin and customize it.
Unlike a venture-funded SaaS application there's no meaningful commercial incentive or issue with building something that will eventually get sherlock'd b the application vendor in the future.
There, I've saved you more millions.