I worry about this too. Diversity is a good thing. And when we do email, DNS, Web, calendars, chat, meetings, storage, etc. all on the same platform, how will we operate/communicate when it fails?
Heterogeneous computing environments provide diversity to isolate and contain failures. So when email goes down, we can still chat and meet.
Teams is so tightly integrated into the MS ecosystem and 365 that it can essentially bring down email and even office apps. Example: PP decks always want to open in Teams by default; every meeting in outlook wants to be a Teams meeting, etc.
Luckily, short of a DNS or auth problem, my experience is that Teams is just an alternate GUI for what already exists - Exchange, SharePoint, OneDrive.
And to be fair, you can just tell Teams to open in the desktop office apps by default (settings > Files and Links), and Outlook has a little radio button to turn off whether meetings are also Teams meetings. All the enterprise productivity apps seem to accumulate complexity and resultant scar tissue, usually in the form of busy settings or painfully opinionated defaults - painful when the defaults don't optimize for your use case.
Heterogeneous computing environments provide diversity to isolate and contain failures. So when email goes down, we can still chat and meet.