headphone outs on these older amps were never an afterthought really. music listening was much more cherished and cared for during the 70's and 80's untill the HT became mainstream. they just ensured that headphones don't fry by putting a dropping resistor for both the left and right channel between the power amp section and headphone out. these older amps have more then enough juice to power about any headphone you stick in the the headphone socket.
I'm in agreement with you. Even the Bottlehead is probably similar in design. It has two 120ohm resistors on the headphone jack, when you remove it you do get more "volume" and more attenuation but a lot more hiss and hum. Sounds much better with the resistors in.