Not true. In the default case, Grandma's wifi router is just passing along -- via DHCP -- the IP address of the cable company's DNS resolver to Grandma's comput

Not true. In the default case, Grandma's wifi router is just passing along -- via DHCP -- the IP address of the cable company's DNS resolver to Grandma's computer. Which the wifi router itself probably obtained via DHCP or a similar mechanism from the modem. This is in no sense a "local DNS resolver." If Grandma has a grandchild that knows how to set up a PiHole, it's a different story. But that's certainly not the majority of Grandmas or the majority of wifi routers.