I'm not sure how this relates to Teams whatsoever and why you're drawing the comparison. Teams is for organizations who have Office 365. Duo is person to person chat... think Apple Facetime.
It's funny, because a friend of mine wanted to video chat yesterday. I wanted to use Hangouts, but he doesn't have an Google account (he's a director of his own company so he lives and dies with the company email), in the end he said: - No problem we'll just use Teams. Not having to create an account was kind of mind-blowing for me (in the "where's is the business incentive in not taking my email, and spamming it?!" kind of way).
While I don't see too many people take advantage of it, you can make a Google account without an associated Gmail account. You just have to choose "Use my current email address instead" on the signup page[1].
https://www.skype.com/en/free-conference-call/ has had web video calling with no sign up for years now, although they were terrible at advertising it, because when they re-told everyone last week it was reported by almost every tech site as a new feature
Please read what I said again, I think google should move more towards an integrated application that has several different kinds of communication modes in it vs. half a dozen applications in various states of languishing, usability, and availability.
I can't call up my Mom on Teams. I can with Duo.