Teams is just an incomprehensible version of Discord. What's the open source version of that? Matrix?

Yes, but only in Europe, and no Americans are allowed.

Do you like work for Microsoft or something, you’re all over this post

You’re way off here. Microsoft are the industry leaders in this space because they’re so far ahead of everyone else because they focus on this stuff. They’re far from lazy, they’re the opposite in fact. As someone who manages the whole MS suite from entra to dev ops all the way to managed instance dbs and defender and everything in between daily, their integration across everything and their pace of updates is insane.

What products specifically are you calling “outdated junk” and why?

Teams is just a copy of old functionality. It doesn't offer anything new. Especially considering their funds and reach. Yet it just promotes the old document / paper world. I'm sure that is intentional. As they need to keep office going. The world should have moved on from documents by now.

What on earth are you talking about by “promotes the old document/paper world”?

Today, when people deal with information digitally, we should be in control in the way we need it. Individual pieces of information should be easy to send, edit, automate, consume and share, without IT getting in the way. Sadly the old files, silos, incompatibility, and systems designed for printing paper documents is still dominant. MS need that. To keep their dominance from the days when they grew powerful and got caught abusing their their monopoly position.
We need to move past this mess as soon as we can.

You wrote all of that without actually saying anything.

How does any of….. that….. apply to this situation? Microsoft are one of the biggest pushers of “all digital” there is.

Their priority is sustaining profit. Which needs them to keep the status quo, not innovate. Teams is not innovation.
If you are satisfied with what we have today, the next generation of digital information will really surprise you. Yet it would have been available 30 years ago if not for big business monopolies and lack of imagination among techies.

Again - you’re writing a lot but saying nothing.

What exactly are you talking about? Give specifics. What exactly are Microsoft “holding back”? How are they only keeping the status quo by having the most integrated all-in-one ecosystem on the market?

I’m not sure why you expect teams to be innovative in the first place?

Surely you want to have good digital communication? And surely you want Teams to help people communicate really well?
But it sounds like you are satisfied with Teams. It appears you have low expectations of communication.
You've read the problems people have posted here. Such as when working with multiple companies different teams. So as a starter, a choice of teams clients is missing. Next, teams is not an open standard. To allow connection with other non Teams networks. Next, Teams attempts to integrate your information. But only allows files pictures and text. Information is so much more. It could be a date, an invite, an invoice, a question, a holiday, an insurance.
If it helps, understand that non IT people want to manage this information in a direct, non IT, non text way. MS products rank very low in this regard.
If all you can imagine is what MS has, then maybe you might understand when it's put in front of you.