Just because something is old does not mean its value is (now) negative. Or are you arguing that "everything older than arbitrary date X is by definition broken, not scalable, not secure" or something?
You can have technical debt today from new code you wrote yesterday, when what you wrote for PHP 8 suddenly gets neutered because someone found a massive security hole and the PHP team deprecates a library function from the next release (yes, this is a contrived example). And at the same time, there will be code you wrote for PHP 5 which is still valid and doesn't need to be reworked.
There's a balance to be struck. If someone always (unconsciously) uses "I" when talking about something, people can wonder if they're a lone wolf or if they're taking credit for what others did. If on the other hand, someone only uses "we", then maybe they're not promoting their own capabilities (or they have little to offer). Reality says that you need both in most senior scenarios other than perhaps cookie-cutter jobs - you need someone who can achieve things on their own, but also work well with others when called for or needed. Experienced candidates often use both I and we when talking about work to indicate that they achieved certain things themselves, but also that they recognise it was a team effort overall.
Not that I think AI has a snowflake's chance in hell of telling the difference.
If I accept your premise (and I'm not saying that I do), where do you draw the line? I quote:
Just that Microsoft can't give it away to kill off the competition.
So can they give it away if they don't use it to kill competition?
What if they CLAIM they aren't?
What if it was only text like IRC? Or only voice?
What if it's something no-one else offers - they have to market it completely independently because they have a successful long lived product with which it integrates well?
Thing is Skype for Business (which was previously Lync 2013 and 2010, Office Communicator 2007 R2 and 2007, and Live Communications Server 2005 and 2003) does text, VoIP, desktop sharing, PSTN integration etc. Has done for years. Teams under the hood seems to be Skype for Business 2020 with a new client though everyone denies it. As far as I can see, Slack just does text, file collab and VoIP, and you need addons for PSTN voice, conferencing etc. Where are the Slack desk phones? The Slack conference phones?
As for Slack itself - the client sucks IMO (as a very seldom user). Click on a conversation to view it and it shows up in barely a fifth of the window. Seemed to be no way to make it bigger for a long, long time. It is as slow as, or slower than Teams (and that's a high bar). Individual chats or channels, no group chats that I see (but I'm not a paying customer, so
Center meeting at 4pm in 2C-543.