Not saying it's a failure, but so far Blizzard clearly failed to impressed a new audience or even potentiel returning players like myself.While it is a good indicator, its not always a direct correlation. From what I remember, OW was never really that popular on Twitch compared to other multiplayer games. Even back in 2017 - 2018 or so the game would usually be under 40k viewers.
It is weird some people are trying to call this a failure just because the game goes back to its regular viewership after beta drops. While I have no data, I would bet a lot of viewers on Twitch watch streams for the streamer rather than the game. If their favorite streamers only played the game during the beta release, they're not going to stick around and watch other streamers still playing the game. Some probably will, but most will not.
That and probably a good amount of those 1.5 million people don't regularly watch Twitch anyway, and just wanted the beta.
It's the sequel of Overwatch we're talking about, not just any game. The original was a juggernaut back in the days so of course people have high expectation for this one. And IMO the twitch numbers reflect that the OW2 beta did not met expectation set for the sequel of one the biggest competitive fps ever made.
And maybe that's on Blizzard for calling this "Overwatch 2" but that's a different discussion.