Ok, how about my tractor costs as much as some cars, does that make it anything other than an expensive tractor? No, it does what it was designed to do exceptionally well and I don't expect it to be a car.
While headphones require less power they are also FAR less forgiving of noise. It also requires an entirely different design to deal with the varying impedance/load that headphones can present to the amplifier.
Look, if you think the 307A is expensive that's a fine and justifiable position to take. But to back that statement up with
is completely in appropriate. You're using power as the basis of your comparison. You should have stopped with "my bad".