I don't disagree with you, but I'd like to point out that iOS apps have long been able to render a view on a television (via an AppleTV) while also rendering a different view on the device screen. This has been possible for at least 4 or 5 years.

There have been a few party game apps that allow a person to drive the game on their device while the other participants see what is on the TV. I don't think it ever really caught on; perhaps partly because AppleTV was a niche product way back when and partly because it didn't get much advertising.