Much of the time, your definition will prevail. But what we found in our first version, is that in a significant percentage of occasions, people do tend to put a little more effort into a note knowing that they intend to share it.

It's like when you type out a quick email to your team linking to a competitor and giving a little context. That's essentially what a shared note looks like. The reason we believe it should live outside the inbox, is because the inbox is designed around time-sensitive content - not content that needs time to gestate or be talked about.