Shocking news everyone! 5GHz-capable wifi devices are faster than 2.4GHz-only wifi devices, even when you plot it by device model.
(I don't know why some specific device models seem to show a mix of 2.4GHz and 5GHz capable features. I think we might be mis-detecting it in some cases. 2.4GHz-only devices reliably show up only as 2.4GHz though.)
The most common device type is "unknown." Oh well.