ZigBee unusable in area with saturated Wi-Fi from neighbors - Seeking advice on 433MHz as an alternative

Are you sure your problem is not the antenna to close to your usb3 port? I live in an area where wifi is really crowded, but my zigbee is strong. I had problems when the antenna was not placed good enough. Try repositioning the antenna, use a long usb extention lead before you abandone your zigbee completely.