I've never heard it called scrotal fatigue, but I know exactly what you mean. A jock (custom made in my case) has been essential for me since my teens, and since then I hardly ever gone without. Without one, the lack of support means discomfort and a dull groin ache almost immediately, quite apart from the soreness and friction which follow. I tried wearing a suspensory a few years back, but although it supported my balls pretty well I still got groin ache, and I looked pretty 'obvious' as well. I need the whole set of tackle supported and held in.
On a few occasions I have wondered whether wearing a jockstrap day in day out means that my groin muscles are weak from lack of use. One or two people have suggested I try going without to train the muscles to cope. But my attempts to do without it have been so bad that I've given up.