Two Mac minis on gigabit Ethernet stuttered through a 2.8 Mbit/s video file because macOS kept using Wi-Fi, and Set Service Order doesn’t reliably stop it. Six Colors’ fix: leave Wi-Fi on — AirDrop and Continuity need it — but in Wi-Fi settings open the ellipsis beside each known network and uncheck Auto-Join. The cost is joining by hand when you undock the laptop.