I would agree that the loudest human vocalization is probably much louder and therefore more audible at mid-to-high range pitches (my own voice seems to confirm

I would agree that the loudest human vocalization is probably much louder and therefore more audible at mid-to-high range pitches (my own voice seems to confirm this). But the loudest human vocalizations are not relevant in the vast majority of conversations, pitch notwithstanding. For example, most people reading this comment would probably attract a significant amount of negative attention if they emitted a sound near their maximum vocal loudness. But at an equal sound power level in watts-per-square-meter, low sounds tend to come through better -- human hearing sensitivity drops off below 100 Hz, but the lowest male voice is around 80 Hz, so that's not usually important.