I think it's 'broken' for anyone who doesn’t use it regularly. It’s too undiscoverable, and too easy to invoke accidentally, for the rest of us.

It’s changed. With the last iOS update, the gestures changed slightly - they used to start with a slide over that could be docked, and moved to a split and/or dock based on the position on the screen.

Individual app’s capabilities also vary based on whether they are windowed or not. For example, you can’t airplay out of YouTube unless the app is full screen (even though once you’ve moved it to your Apple TV, you can switch away freely).

Discoverability is also crap. You have to dig into the manual (which you have to “buy” for free) to get the full details of the feature.