Well, it's not free (or gratis) is it? It just happens to be included in the azure ad/o365/exchange plans? So, if you're on gsuite, for example - ms teams isn't "free"?

This. At work we use it because it is already included in our Office365 subscription, but it is so painfully slow. Really, unbelievably slow.

Same is true for Google Hangouts Chat and you don't see anyone using that...