Sorry, I imagine you posted this before my edit. I don't think this marketing video contradicts my point at all. For Microsoft to commit a large amount of dev time to rewriting Teams and improving its performance, there must have been an actual business reason. That's not something you do because some nerds on HN think your app is too slow.

Presumably, Teams was so unbelievably slow that it crossed over to being an actual problem for customers and not just a mild nuisance. So Microsoft improved performance just enough to stop affecting sales. Is the performance _good_? No, it's still comically slow. But there's simply no incentive to improve the performance further.