In the speaker world a 16 Ohm impedance is on the high side. Today many speakers have an impedance of 4 Ohms, made possible by the high current and high power solid state amps available now. I don't know whose point this supports, but it argues that high impedance (for a loudspeaker) made a better match with the low power low current tube amps of that period. The high impedance loudspeaker was made all the more sensitive by their high impedance. I understand that for headphones 16 Ohms is a low figure.
I gave you an example of the value of high impedance for speakers . Why are there headphones with insane impedances of 300 or higher Ohms anyway??? I don't think it is a match for low power tube amp. I hope someone who does can chime in here.