Longer-term I think Notion would benefit from going straight for the Google Workspace/O365 market and start offering email/calendar/etc end-to-end, rather than their current strategy of integration. The current strategy makes sense to start building up the suite, but: Google is feeling increasingly vulnerable, Notion itself is one of those rare products that has maintained general positive vibes among its customers for many years, and I think a lot of especially smaller companies would opt for just the notion suite if it checked the major boxes.
I've also always felt that Dropbox should have went down this road, after they released Paper in 2015, but I think their time has passed. Google also wasn't nearly as vulnerable back then; they still aren't super vulnerable now, but I think they're trending that way, and if Notion times it right they could be in a great position.
Competing against that market would be extremely difficult. These are two well entrenched companies that their lock in makes switching from extremely difficult so you would be forced sell to new companies which means revenue early on would be very low. Also, if you don't have 100% compatibility, they will throw their hands up and switch to one of established vendors.
Yeah the Google/MS tier of integration is not the level Notion can play in. But being good friends to those integrations means they'll win against all the other productivity SAASs that get thrown around at any given company.
I honestly thought Salesforce was leaning this direction with Quip and Slack. Granted, Quip was never a good product. So I guess that fumbled.