As far as i understand only usf distributing heals all units in range simultaneously, while other factions' heal do it by models. So, advantage is: heal everybody at once, disadvantage - no auto heal. My point is - deal with it, it's calling a balance.
That is relevant only and exclusively if you blob only and are forced to mass retreats.
The playstyle current ambulance ENCOURAGES.
It also enforces another micro task on the already micro intensive USF. You can't even do weapon upgrade without additional micro other factions doesn't have.