I was a developer on versions 2 through 4.5. I agree with the main point of the article: Lotus Notes was breaking new ground, and we sometimes landed on suboptimal designs because we didn't have a prior example.

And once we had a design that the current userbase was used to, we couldn't change it easily even if the rest of the industry standardized on a different pattern.

But Lotus Notes's main strength--everything is a database, even email--was also its biggest UX weakness. The "email app" in Notes was built in the same low-code environment customers used to build custom apps. That was good because email got features like encryption and replication for free, but it was bad because we couldn't easily customize the UI to optimize email. Instead, we had to add general-purpose UI features to the platform and then use them in the email app. But that was more work and took longer. Outlook could improve faster.