This discussion really has nothing to do with equalizing for room acoustics or speaker inadequacies. A loudness control's purpose is to compensate for the ears varying frequency sensitivity to different sound levels.
The good thing about variable loudness is that it's volume dependent. Equalizers are not. What sounds right at 85dB probably doesn't at 65dB and vice versa. When I used an equalizer with a preamp that had variable loudness I used a meter and test tones to measure and adjust at my highest listening level. I used the loudness control to lower the volume from my personal maximum. My only reason for ever having an equalizer was for room Eq. I never used it as a constantly tweaked device. Measure twice and set once was my method.
My comment was actually for savatage.