What do you do in valet when the guests come all at once to pick up their cars?

I'm at an event doing valet and there's about 250 cars and 20 valet guys working.

The party ends and everybody comes out all at once. Usually people leave slowly or normally. Not all at once.

So the guests then have to wait patiently and they complain we're doing a bad job all the while we're running our butts trying to bring them fast enough.

Are the valets guys at fault?

I don't think so. But what can we do to better the situation?