Having just received my brand new Surface Pro 7, I was experiencing the same almost non-existent wi-fi download speeds on all wi-fi networks at all times. I found the solution to my problem. On my system, if the Microsoft Wi-Fi Direct Virtual Adapter is not enabled (i.e. not listed in Device Manager under Network Adapters), my download speeds were pathetic. On the other hand, if the Microsoft Wi-Fi Direct Virtual Adapter appears in Device Manager, I get proper download speeds.
As best I can tell, the only way to get Microsoft Wi-Fi Direct Virtual Adapter to appear in Device Manager is to either (1) be actively projecting to a wireless display (obviously not a suitable option) or (2) change the option in All Settings | System | Projecting to This PC, to allow other devices (with your permission) to project to your device. This option enables the Microsoft Wi-Fi Direct Virtual Adapter. You'll need to adjust the other related settings if you want good speeds on all networks (even unsecured ones) and/or when your Surface is running on battery.
This is obviously not an ideal solution, but at least its a good work-around until Microsoft and/or Intel fixes the buggy wi-fi driver.
Hope this solution helps others.