A powerful radio signal will interfere with neighboring devices even if they are on different channels (frequencies). I don’t mean to derail this discussion too far off anymore but my last comments regarding Wifi congestion:
1. You cause congestion on your Wifi network by utilizing high Tx power from your wifi device
2. Your neighbors cause congestion on their Wifi network by utilizing high Tx power on their Wifi device
3. To minimize congestion on YOUR Wifi network lower YOUR Tx power
4. Your neighbors minimize their Wifi congestion by lowering their Tx power
All I can say is to try this if your Wifi device offers Tx adjustability, which most all in one router-firewall-WAPs do these days.

