I’d say Chromecast is the only flagship there, it’s everywhere and reshaped the genre of those devices.

I used Stadia, it was cool, but clearly something they were dipping their toes in, it was never popular.

YT Originals was fine, but again not popular. Cobra Kai was the only show I really heard about.

I’m not sure how popular Hangouts was, I used it extensively, but only within certain groups of friends. It had no way to make money though, and they have made a bunch of messaging platforms since.

None of those were even close to flagships, they were all short term experiments.

YouTube is the basis for much of Google’s portfolio and a steady moneymaker, not an upstart liek those.