If the attempt to reinstall the WiFi firmware eventually resulted in message "Failed to connect at any baud rate", that is enough evidence. It should normally connect at the first baud rate that it tries.
PS - I forgot to mention: make sure the Duet has adequate power when trying to upload WiFi firmware. In particular, a USB port on a laptop may not provide sufficient power if a panelDue is connected. It's best to use VIN power.