Royal Arches is an awesome route. It is pretty easy for the most part but it is 14 pitches (50m rope lengths)long and if you take too long you are either rappelling some 14 pitches (not he route but hagging rap stations to the left of the climb with a bunch of trees trying to snag your ropes)in the dark or trying to find North Dome Gully in the dark. NDG is straight forward in the light of day (there is only one spot where you may want to rappel) but in the dark it is a KILLER. They did the right thing to stop and bivy.
Many climb in Yosemite are quite committing and you always need emergency gear even in summer but you can't take too much or it hinders climbing.
They probably started too late for son's experience. There is always a line up even at dawn.
The time I climbed the route we were at the start at 5:30am waiting for first light. We even climbed the starting pitch in the half-light. We topped out aroung 1:30PM and were drinking beer by 4 at the Awanhee Hotel Bar.
Not to sound to harsh but getting rescued by YOSAR is an embarrasment; I would call YOSAR only if I thought I was definitely going to die. Most climbers have a self-rescue philosophy but in the recent years a lot of folks have become soft. These guys whimped out. They should have waited for first light and found the North Dome Gully.
If they were going to climb to the rim of the Valley in mid-April they should have expected a possible epic and prepared better.
Late start, too long a rope and the BS walkie talkies had everything to do with their problem. They should have used as shorter rope (the route was put up using a 50m rope; they had a 70m. This is inefficient.)and left the electronics. That way they would not have had to get YOSAR to come get their sorry butts.

I have personally witnessed the walkie talkie climber type fumbling the whole way up a route and wasting time talking to their partner. They should learn the old school proven method of yanks and tugs mixed in with a lot of yelling.

I am a memeber of Supertopo.com but have not been visiting the forum as of late. I was suprised to see how encouraging the responses were a few years ago they would have got flamed like crazy.