With the router at the heart of your network, all traffic goes between your device and the router. These point-to-point links are the same for computers, game consoles, thermostats or wall switches. If something obstructs the WiFi signal path, there is no way to "rearrange" the network without removing the obstruction or moving devices around.
While Z-Wave uses a more robust mesh topology compared to WiFi's hub and spoke, messages are sent in a routed fashion. Each device participates in a fire brigade of messaging dominos where a message will begin on one end of the network and transit through multiple devices to reach its destination. This helps with potential obstacles but adds latency. And if one of those middle devices goes fails or goes missing, the network has to work around the broken link, further adding to the latency.
Messages in the Insteon world are sent in a very different manner. Instead of point-to-point or routed links, Insteon devices broadcast their messages over the entire network. All devices then repeat the initial broadcast three times and with each repeat, every device on the network repeats the message in sync. The result is a bombarding cascade where the device in question hears the message from nearly every single device on your network.