Thank you @Alexandre. and @Philbert for reading my details and for the prompt, thoughtful responses. I was also puzzled by the backhaul issue and assumed it just doesn't work in my configuration...

I have 3 DECO X60s for my home's mesh network, but I use Verizon FiOS for internet access and it was delivered via Coax, which required me to use their Verizon G1100 router. So I've kept the WiFi...