The article probably came out in the early-mid-90's, which is when I subscribed to PS for a number of years. I'm sorry I can't be more specific than that -- having it in hand would be far more useful to this conversation than my vague memory.
But you're right, by that time roller furlers had become almost ubiquitous, so more folks were often opting to sail under jib alone for simplicity -- and apparently an inordinate number of mast failures had been observed with this sail configuration.
We're taxing my memory here, but as I recall, they looked at a lot of different aspects of rig geometry and sail combination when they were trying to find a common denominator, which as I previously noted turned out to be rigs that had only single lower shrouds. I also recall that the failures experienced were in the mast section, rather than in any of the shrouds or stays. That is to say, the mast snapped without any precipitating failure of the shrouds and stays. But these mast failures were occurring under jib alone -- there was no similar pattern under other sail combinations. I don't think they did any comprehensive analysis or comparison of other types of rig failures under other circumstances in that particular article.
One circumstance you mentioned was backstay failures, and I would just add it is my experience that backstay failures are not always as catastrophic as upper shroud or head/forestay failures, provided the mainsail is up. If the main is up some of the load borne by the backstay can be carried through the leech of the sail and then to the deck via the boom and mainsheet system. As you well know, many racing rigs sail with their backstays completely or very nearly slack in light air. Some of that load is absorbed by rig geometry (swept back spreaders and shrouds), but the sail and sheet are a factor as well. [I'm not saying backstay failures are inconsequential, only that they can sometimes be managed with quick action (turning upwind, getting the jib down, and leaving the main up sheated tight until halyards are led aft).]
In the PS article, they concluded that this load-bearing aspect of the mainsail and sheet somehow offset the rig stresses that occurred under jib alone on boats with single lower shrouds. Unfortunately, I do not remember why, and I am not qualified to speculate.