In larger scale systems (say ham radio or commercial radio or cellular telephone) there is some network planning involved. A ham radio repeater on a mountaintop can “network” with another repeater 70 miles away if there is a good line of sight. Similarly cell phone towers use millimeter wave and other radio backhaul but once more there is a carefully planned line of site. That isn’t what is happening with mesh WiFi.
Sure, they don't use bands requiring line of sight (though you can buy relatively cheap fast point to point wireless that's line of sight), but a mesh WiFi router that has 2.4, 5, and 6 GHz can reserve one for back haul.
