What I am saying is that there are lots of things in play, so the less variables the better. WiFi works differently depending on which device is connected, local interference, etc. A smartphone might give a better or worse result - for example I have a HTC M9 that connects at 400 Mbps to my 5GHz AP, while an older laptop connects at 140Mbps. A newer laptop connects at 400Mbps.
If you get to test a gigabit connection (like the one I have at home) using the older laptop , one could wrongly assume the ISP is limiting speeds, when in reality is not. Ethernet removes these variables immediately.
Also you already conceded you're in a fringe coverage area. This mobile technology will be affected by distance to the site and by the number of people connected to it. The more people connected, the smaller the coverage area is, which means that at some times users in fringe areas will see a loss or reduction of service.