Agree with that, I've used both Notes heavily in the past and SharePoint/Exchange as a software engineer exposed to them and Notes always felt more cohesive. Notes (and Oracle products) get dumped on in discussions on Reddit and sometimes on HN but Notes worked well and was very consistent, Oracle products too for that matter, in my experience.

Notes and Sametime also worked very well on Linux on my IBM work laptop, supported by support, official Linux distro inside IBM. That was mid-late 2000's when many companies hadn't even thought of trying to support both Windows and Linux (or Mac).

Sametime had to work in Java Applets so portability was key. IIRC our biggest customer was the Australian navy.

I was briefly what is now called a developer-in-test on Sametime after Lotus Development bought them. I was untrained in C++ so my bug reports for that API were frequently closed with the comment "No".