Zigbee devices sometimes have problems in fixed location setups, such as light switches, because WiFi can drown out zigbee. So the stronger you make your Wi-Fi signal, the more likely you are to lose your zigbee messages. This is probably the main reason why zigbee Has not been very popular for do it yourself residential light switches. It is used in commercial installations, including office buildings, but they tend to use a lot more devices per room and professional installers have tools to help locate and deal with potential interference which are not available with SmartThings.
Lutron uses its own proprietary protocol which is in a different frequency range and does not have these interference issues. It is not using a mesh, but it generally doesn’t need one.
In my own home, I use Lutron Caseta switches and zigbee sensors. I like both protocols, but Lutron is an engineering company focusing on lighting. They hold many patents and as an engineer, I just really like their devices. But Lutron doesn’t make standalone battery operated sensors, and I find zigbee is a very good match to that use case.
So there are certain people who are using zigbee light switches successfully, you Just need to be aware of the potential interference issue.