I think Z-Wave is a bit more open now but everything I’m seeing indicates Zigbee has pretty thoroughly killed it by not requiring arduous certification processes and being generally easier to work with. Z-Wave is technically superior with the ability to have devices directly communicate with each other for basic functionality but at least for me that wasn’t worth the massive markup and I’m slowly replacing anything z-wave with Zigbee equivalents.

Zigbee supports binding, allowing devices to directly control each other without the intervention of a controller. For example, I've Inovelli light switches that communicate directly with Zigbee smart bulbs.