If you can connect everything without using the router, that is the way I would go as adding another device just complicates things and more places for things to go wrong. I prefer using my own modem and a separate router instead of a gateway. Not sure if that is an option for you.

@Oldtreker. 

 

If you happen to have a dead zone still you can look to set up the C7 via WDS bridge. However, if your network is still running well I would keep the C7 in case the Wi-Fi goes bad on the AT&T or if the extender dies.