I don't quite think so. AirPlay is a proprietary Miracast, long before Miracast existed. Although it's proprietary and the payload is protected with DRM, Apple uses it as an encrypted tunnel between approved (and first-party) devices.

Meanwhile, Google Cast is a media-streaming negotiation, handoff and control protocol marketed as a wireless streaming solution. It's not so much about packets on the wire as control commands and metadata. That, I feel, is a significant difference.

Chromecast is available on iOS and the web, not just Android, ie any third-party iOS developer - not just Google - can support Chromecast.

So platform support is more widespread, though your main point is valid insofar as Google determines which platforms it works on.