Well to figure out the real speed iperf3 is your friend: [How To] Check Network Performance with iperf3
Do you have seperate SSID’s for 2.4 and 5Ghz wifi? If not you might actually be connected to your 2.4 Ghz network
You can configure from command line with connmanctl but surely while you are logged in via SSH it might be tricky to change your network connection as you might loose connection.
Being that close can lead to interference that lead to connection issues.
I would stick to cable as it should be good enough with the Kernel mounts.