I fly out of JFK T4 often, before 8 am there are lots of empty seats. In the evening (with lots of intl flts) the lounge is crowded, but the few times there were lines they moved rapidly.
T4 is a large terminal with the AMEX CENTURION lounge very close to TSA security, that lounge's location helps to draw pax away from the SC (assuming they head there first). The SC is near gate 32, due to the large walking distances pax dep from (say) gate 24 might not even choose to use the SC--TSA c/i to 32 (back) to 24 is lots of walking.
[PS: I can't remember every seeing ALL the moving walkways working...]