WiFi is not good for a network with lots of devices. It's star topology which limits multi-device performance. And the WiFi AP which can carry many devices is expensive.
Many WiFi smart home devices only support old WiFi standard, it will pull down both performance (If there is a old standard device, the AP have to fallback to old behavior to match it. OpenWRT's setting also inform that.) and security (You can't use WPA3 only, even WPA2/3). And because these devices use the same network technology with your home network, you need something like VLAN to isolate them.
I personally see that as a feature. When I was researching what route to go (wifi/zigbee/zwave) I encountered enough horror story posts about mesh networks to know that it's not for me. Small network absolutely, especially for battery powered devices, but meshes seem to hit critical mass where it becomes unstable & then people end up doing stupid shit like having to physically uninstall wall light switches to temporarily move them closer to hub to re-pair them
Adding more 2.4ghz AP capacity is comparatively trivial. Hell even raspberry pis can act as APs.
>it will pull down both performance
Anything where I care about performance is on the 5 and 6 ghz band. 2.4ghz is too noisy in cities for general use, but is entirely adequate for IoT sending a couple bytes every now and then.
>[WPA] security
That one is indeed a problem. At some point I'll stick them on a separate AP device with a firewall between that and rest of network, but can't say its a priority
Many WiFi smart home devices only support old WiFi standard, it will pull down both performance (If there is a old standard device, the AP have to fallback to old behavior to match it. OpenWRT's setting also inform that.) and security (You can't use WPA3 only, even WPA2/3). And because these devices use the same network technology with your home network, you need something like VLAN to isolate them.
It's whole terrible story.