FWIW, before the early 1990's, Ethernet usually meant stringing coaxial cable between desks, and computers would have a BNC connector on the back which would have a BNC Tee fastened to it. As I mentioned before, Ethernet over UTP was an early 90's thing. Installations from that time were usually connected to hubs, which meant only two stations could be communicating at any given instant. Switches became common in the mid to late 90's, which allowed for much higher traffic flows as multiple station pairs could be exchanging data without interruption.
Bottom line is that if I have choice of getting on a network with Ethernet or WiFi, I would pick Ethernet almost every time. As for adapters, USB 3.0 or 3.1 would would not support anything above 2.5G.
I would agree that putting an Ethernet port on an MA wouldn't make sense, but an MBP is a different story.