Just because a device uses wifi doesn't mean it's not proprietary nor does it mean it is easy to integrate with other devices who use wifi.
There are more wifi bulb brands than I care to remember, and every one of them come with their own app. The only thing that sort of works if it is a OEM from Tuya, then you can use the Tuya app.
Z-wave has one great thing I enjoy: Direct association. I can (with almost any z-wave-controller) tell lightswitch A to talk directly to light B.
The problems with Z-wave are several though.
The mess with unsecure/secure inclusion and communication. Device A can't communicate with device B because.. something.
Firmware updates that are not published, so to update a fibaro device I need a fibaro hub. Likewise Aeotec.
So many darn command classes and various support
Some cheap devices, like a dimmer I own, doesn't report back to the hub when I turn the light on using the dimmer. This might be due to point 1 above.
Maximum 4 hops. I believe zigbee has 10. Or 5? If you have a larger house that might not cut it. It helps to "reconfigure" the network, but still.
I have 20 or so z-wave devices. They mostly work. Temperature, motion and lights. But I've started to add a few shelly devices, tuya lightbulbs and tuya outlets for cheap effects and power measuring, because while a z-wave device usually costs $40/40 euro and up, Tuya bulbs and outlets can be had for $10.
But then I've started to feel the need for a IOT Wifi vlan, so I have to do some work to ensure that works..
Home Automation sure takes time and money