I've never used Teams, but it seems like an awful lot for one app to handle. But the Google way of splitting it up across the logical apps seems to work well, since everything's integrated anyways.
At the end of the day, does it really matter if you're using different icons in your home screen or different icons in a menu?
When Google releases a new product, it's like the almost expect you to use it in isolation, but with your same account. And they love releasing new products. Google Calendar, Tasks, Keep, etc.
Microsoft Teams brings together Office 365, Exchange, Share point, OneDrive, and then adds collab features on top for comms and organisation.
You get your full existing Outlook Calendar appearing in teams, you get all your Outlook contacts, you can link to any doc in your OneD, shared edit, you get group chats and channels, you can create "Teams" (where the name of the app comes from) made up of different people in your Exchange org.
For anybody using Microsoft AD/Exchange within their org, Teams is a natural choice. You don't need a new account, everybody else in the org is immediately searchable and contactable, there's no data import needed. It just works. And "it just works" has been the central driving feature of anything that has taken off during this lockdown.
But I guess I don't see how Google apps are "in isolation", it's the exact opposite. All my contacts appear in every app, whether Calendar or Meet or Docs. Links work everywhere. The Google concept of a team is basically that when you create a Group you can generally use it everywhere else (to share a doc, to create a calendar event, to add to a Team Drive, to start a chat, to notify of a comment, etc.).
And heck, the "side panel" functionality literally allows you to load Keep inside of Gmail, or Calendar inside of Docs, if you don't want to open a whole new tab. Clearly the opposite of isolation.
Maybe you've just never used Google apps this way, that you haven't seen their integration? I find it entirely natural to have a tab for Mail, Calendar, Keep, Tasks, and several Docs and Sheets in my browser. Perhaps for me, my tabbed browser window is the same as your Teams app?
In either case, it seems like the functionality and integration is largely identical. Again, it's just a matter of whether the icons are at the browser tab or home screen level, or whether they're inside of a single app. It seems to be a very minor distinction at the end of the day.
Now that we've all been forced to use it and come to terms with it, the deep integration is extremely powerful. In fact the couple areas within it where the integration is still a little thin stand out because the workflows around those end up being a bit fussy.
It can be difficult to explain to somebody who doesn't use it, but it's not something Google has sorted out yet, not even close. It's like saying "I have all the ingredients for a cake in my pantry, so they're all together, it's basically the same as having them together in cake form."
Google has all the pieces to do something even better than this, but their corporate culture is like a hammer shattering all the pieces into different bits with only the most superficial connections between them. They may be allergic to even try given what happened with Wave, but even a half-decent copy using the building blocks they have would be pretty great.
What is missing is a way to sort through the threads (no title, no list of threads, no way to jump to the ones you have a notification for…). And probably a way to sort the rooms too; I'm part of 23 rooms and it's all over the place (and growing).