The Scarlett app actually does run on it's own on the TV. The phone is required to just get it started by casting. Plus if there is anything you want to play/skip, instead of using the remote you can use the phone.
Works by casting from your Android phone to AndroidTV.
Videos of how it works and features here .
Why not make this as a daydream app native to androidTV?
I was intrigued by the idea, until I saw its driven by your phone. I want my TV to be a standalone device. It doesn't need to pull content from my phone when it has its own internet connection.