Nobody with decision making power actually cares whether any of the software in use in enterprises works well or not.

^this just isn't true. There's three camps of people. 1) The people who use Teams today and think it works just fine, they even enjoy it and find it simple to use (these people exist). 2) The people who use teams but are annoyed by many small issues that together cumulate to a poor UX. 3) People who will never like Teams for many reasons but make a point about being as vocal as possible about their hate.

Decision makers and leaders care about 1 and 2, which imho is good. I do agree that Teams isn't perfect and I also agree that it plays best, for now, with IT ecosystems. That said, end user love is critical and I think fixing that for group 2 will only help to secure Teams' undeniable comp advantage.