In short: Teams is not all that revolutionary or even great.
Where's the fifteen year old IRC client which does hardware accelerated video chat from a web browser?
> "In fact, today we don't need a document editor embedded in a chat app."
What can be asserted without evidence can be dismissed without evidence. Except we have evidence: given a choice of Teams or IRC, businesses choose Teams.
People chose Skype because it was fast and it just worked. It stopped being fast and people moved over.
Meanwhile, at work, I can't reliably see my teammates in video calls because MS Teams still hasn't figured out how WebRTC works.
* Slack takes 6.5s to load on my 2021 Macbook.
* Slack consumes 366MB of RAM - if I browse around that rises to 744MB of RAM.
For the longest time Slack would kill my machine if colleagues posted gifs in messages. I'm no fan of Teams but I think there's plenty of shame to go around living in a world of eight core CPUs running large Electron apps.