The leader clips the master point before leaving the station, climbs up 5 feet, and falls. Let’s assume the fall is clean, the belay sucessfully arrests (though it is violent), and all the gear holds.
It is a fall factor 2 directly on the anchor. What I want to protect as much as I can...it is my anchor. No anchor and I am death in that situation.
The question is how I can protect my anchor? The question of the force on the pro is not important because one way to rig the anchor is to do a clove hitch on the first cam, an other on the second and an other on the third. In that way, if the first didn't hold the fall, it will take a percentage of energy, if the second don't hold, it will take an other percent of energy and the third have some chance to hold (present in john long with piton).
How I can I protect my anchor is more than an interesting question. Some study show that when load, the harnest took a part of the energy. The energy took by the harnest and rope running true the device can be as hight as 20 %. So, if you belay directly on your harnest, instead of risking your life by using the anchor as a first pro, you have 20% more chance that it will hold.
personally, I use a sliding x on the anchor and I back up the sling with my rope on a protection. If I don't think that one of my pro will hold more than 12KN, I will double it with an other. For example, if my second and third pro was no as safe as I want, I will use a sling between them to a master point and an other sling joining the master point to the other pro. I will use a back up differently.
As usual, what is important is that the anchor hold the fall. If one pro hold 100 % and the other 0 is not more important than if each pro old 33% of the fall. It is superficial rules and that kind of challenge doesn't help to safe life of people. I think that the new generation of climber have a lack of knowledge on safety.(not apply to every climber, some are very safe and have bad advice...)