Earlier quoted context omitted.
Teams is integrated with lots of other products such as AD, O365... It's far from a "basic chat app". I am sure the app you wrote does not have millions of users daily, either.
"I am sure the app you wrote does not have millions of users daily, either" This argument is weak. Its not like millions of people are crammed within the app all at the same time, while integrated with AD, or other microsoft bloatware. It may impress inexperienced devs, but it's really not much of an architectural challenge. MS could have done a better job. But to satisfy your curiosity, my background is in developin…
I think the only inflated thing here is your ego.