But this new one is better! It has two advantages.
Vacation period aside, in the old proposal the chance that any two people share at last one free day is 5/7. In the new proposal it is 100 %. It's one thing to be in some sort of long-term relationship so that one submits applications for off days and vacation with that in mind. Sometimes, you want to be able to make more spontaneous decisions. And with this, you know that any two people can have a free day together within a ten-day period.
The number of groups in the new proposal is lower, and since it is easier to find five people who can do a particular task than to find seven for it, that's another advantage.