It's an interesting point, but I do think something like what was done this year is then needed on a semi-regular basis, to basically smash the large groups apart and allow them to build from scratch with new people.
I think over the past few years we had started to see more and more closed-off large groups, who absolutely initially formed that way, but were by now just focused on looking after each other. And there's absolutely nothing with wrong with that, I would do the same, but at that point you start to lose the community of strangers element and it's just friends helping each other.
There's no need to see it all. Go at their own pace and spend time taking it in. Try and avoid the worst of the crowds and hopefully it will be dry and they can stop and rest their feet whenever they feel the need.
I hope they have a wonderful time.