It certainly is strange that you are experience such a huge difference in speeds from Ethernet to Wi-Fi. Ethernet is definitely faster but from the results that you've provided, it seems like your devices are connecting to the 2.4GHz band and not the 5GHz band.
Do you know if you have Band Steering enabled on the Gateway? If yes, it can be difficult to determine which band you are connected to. For testing purposes, please disable Band Steering and connect to the Network designated -5G. You may need to edit the network name after disabling Band Steering.
Let us know if the speeds are still low via Wi-Fi after trying this.
@osh168 there's nothing that stands out as being an issue, however, your modem is using a DOCSIS 3.1 OFDM channel for the downstream data and the user interface doesn't present all of the data for that OFDM channel. Call tech support and ask the Customer Service Rep to run a signal check on your modem. Ask specifically if the OFDM channel parameters are within spec and what the QAM number is for the QAM channel. It should be running at 1024.
Also, have a look at the following Microsoft support page regarding the Windows TCP Receive Window Auto-tuning: