If you compare the reach of AirPlay against the reach of Chromecast there's a difference of at least TWO orders of magnitude; that's my basis. And I'm not an apple fanboy (gohrt), I'm more of a reality fanboy.
AirPlay is not a device, it's a technology implemented by multiple devices, and it's four years old (compared to Chromecast, which is barely one). Comparing the two directly is nonsensical.