Notion is dense and calm, Discord is dense and loud
What Notion gets right isn't simplicity. It has an enormous number of features and almost none of them are in your way, which is a harder thing to build and a much harder thing to keep.
Everything is the same primitive
A block. Text is a block, a heading is a block, a table is a block, an entire database view is a block. One thing to learn instead of a dozen, and what you pick up in the first week still holds years later.
The menu is ordered the same way. Common blocks first, the powerful ones a small scroll away. I used Notion for years before I found gallery view, and I found it the week I needed it. Those years weren't worse for not knowing it was there.
Changing one block doesn't disturb anything else, which Word and Google Docs still can't promise. So you can experiment without fear of breaking your own document.
Discord makes the opposite choice
Servers, channels, categories, threads, roles, permissions, bots. All present at once, all competing for attention.
That's right for the person it's built for. Someone running a community needs roles and permissions on the first day, and burying them would be the wrong call. The density is an answer to a real user, not an absence of taste. It just means everyone else walks into a room that's already running.
Why I care
It's the principle I work by, and it's easier to argue for when someone else has already shipped the proof.
On the finance product I work on, features start switched off and turn on when a need actually surfaces. Someone who skips setup entirely still gets a working app. Off isn't empty. It's an app without a dozen capabilities nobody asked them about.
Not simplicity, restraint. A core that is complete on its own, with depth available to anyone who wants it and imposed on nobody.
The part I'm less sure about
Design conventions differ by market. Information density that reads as efficient in one reads as noise in another, so restraint isn't a law. It's a choice about who you're building for. I'd still make it. I just can't claim it's the only defensible answer.