I agree with you that their Matter integration is useless. I can confirm all your findings.
The only saving grace for me is that once setup, it is possible to use these bulbs with the Wiz integration, without connecting them to the Internet.
I spent some time in the last week modifying my pfSense setup to selectively block IP and public DNS access from certain devices. That includes my 220 Wiz bulbs, that were already setup using the Wiz app using cloud access. All of them continued to work identically in Home assistant with the Wiz integration.
When the bulbs are firewalled, but the phone isn’t, the Wiz app on the phone malfunctions in the following ways :
a. It refreshes all 220 bulbs every 2 seconds, making it very hard to click on anything .
b. it can onboard new bulbs that are firewalled, but is unable to change the fade-in timeout on any bulbs, whether Internet connected or not
c. the delete device function fails. It deletes the bulb from the cloud account, but does not reset the Wifi credentials. The bulb stays on the network indefinitey, unless powered off.
All 3 issues have a common single workaround : temporarily unblock all Wiz bulbs from Internet access - not just the new bulbs. Then, the app functions as expected. You can onboard new bulbs. you can set the fade-in timeout. And you can reset them. Afterwards, you can block them back, and use them only in Home assistant.
I reported these issues to Wiz support yesterday, but don’t have much hope that they will even understand what I’m talking about, given their initial response. I will follow up, though.
I wish it was possible to set the fade-in timeout without having to use the Wiz app. It might be possible to reverse engineer that setting and do it on local Wifi. At least, I hope so.
Also, it may be possible to use Matter to provision/unprovision the bulbs, without having to unblock them from Internet at all, but then subsequently use the Wiz integration to discover them locally, and get near full functionality.
Only a small percentage of my 220 Wiz bulbs support Matter, and even if Wiz worked out all the Matter bugs, I would still be using the Wiz integration that can work with all my bulbs, especially groups of bulbs, and do things like set the color effects on those groups.
This is only my 3rd brand experience with Matter devices. I have about 80 Yolink devices, and am using them through Matter with a Yolink local hub. There are several bugs and limitations in their Matter implementation as well, which I also reported. The other one is GE lighting/Cync reveal, which I bought this week. That is the best of 3 brands in terms of Matter support. Everything works, except the light show feature, which is missing in the Cync Matter integration. Setting non-animated colors works, though. I am able to set the same color on both my Wiz bulbs (using Wiz integration) and the GE Cync undercabinet lights in one group in Home assistant, and it works well. For white CCT colors, they even match very well. Not close for other colors. Even different models of Wiz bulbs that I use, like R20 and A19, don’t have identical colors.
The common trend for all 3 Matter integrations is that some features are missing in Matter that are available through the other integrations, whether cloud-based for Yolink and Cync, or local for Wiz.