A Thread Border Router acts as a bi-directional bridge between a Thread Mesh Network and your home LAN. Matter uses IPv6 (it creates its own private IPv6 network behind the scenes) that lives on top of Ethernet/WiFi/Thread.
Just like Zigbee and Z-Wave, Matter over Thread devices need multiple repeater-capable devices to strengthen the Thread Mesh Network. Since this requires non-sleepy devices to act as repeaters, the devices need to be mains-powered, just like for Zigbee and Z-Wave. The difference that I see is that most (not all) mains-powered Matter devices are “Matter over WiFi” devices, which do not help with strengthening the Thread mesh network at all. Thus, many people choose to add more AppleTV 4K’s, Google Home Hub’s, or Amazon Echo’s with built-in Thread Border Routers to help strengthen the Thread mesh network. Then the problem becomes possibly having multiple Thread mesh networks, one from each brand of devices, which do not help each other whatsoever. That problem is supposed to get better with Thread v1.4, which has been a slow rollout amongst the big three companies.
Right now, I would agree with you. Sticking with Zigbee, Z-Wave, and possibly Lutron will make for a solid smart home.
IMHO, Matter over WiFi devices are actually somewhat decent and reliable. Matter over Thread is a bit of the Wild West. It will improve over the coming years, but it has some maturing to do to get everything to work together smoothly. The new IKEA devices are a perfect example of just how much more maturing is required.
If you want to read about recent experiences of Hubitat users with those new IKEA devices, start here.