I don’t quite understand the desire for friends or family traveling together to exit the airplane at the same time and hold up others as a result.

Airports have waiting areas between arrival gate and passport control, probably precisely to let passengers traveling together catch up with each other. Even the worst possible airport would have a bathroom, and toilet entrances are implicitly a waiting (queueing) areas.

Unfortunately, introducing any sort of rigid structure and order into airplane disembarkation process sounds like an impossible task.