Yet if I'm on Zoom calls, I can always tell who is on wifi and who isn't. The best wifi in the world will never, ever beat a proper cabled connection, period.
No you can't. You can tell if someone has a poor WiFi or internet connection but you're talking out of you bum if you think working in tech somehow makes you able to tell how someone is connected to their network from a video call.
I've got WiFi 6 in my office, I get 600mbps from speedtest.net on my phone.