I guess FSO weight is fairly unimportant in discussions, to me.
I always use the same clothing for 3 season camping:
Pants, shirt, socks, hat, shoes, staff, pocket knife, map & compass and car key... FSO means simply adding my cloths, staff and pocket knife, they weigh around 5 pounds give or take, always.
I always carry the same base weight for 3 season camping. About 9-11 pounds, depending on what sleeping bag, and thickness of my long johns, always.
Consumables or "live load" in my pack means a LOT more to me than base weight and FSO weight. Water is mostly 2 pounds: 2 .5L bottles. Food can varry...between 1.1 pounds and 2.5 pounds. This means my pack weight will varry from 11 pounds for two nights out to 24 pounds for two week canoe trip. Yet FSO doesn't catch a trip like this, either. None of the definitions will catch the overall loads of walking a canoe on wheels down a trail.
Like base weight for two night or two weeks, clothing doesn't change. FSO is important as an overall definition. But FSO or base weight do not answer the basic question: Where can I reduce weight and still be comfortable? It does not answer where. My cloths? My pack? My tarp? To me this means it is less precise than pack weight. While always considered, I rarely use the FSO definition. I can add in 5 pounds to mine or subtract 5 pounds from yours...roughly speaking I can derive the pack weight. Does this mean I will not change out a my 1 pound, heavy nylon pants for 12oz UL rail riders? No.
But, all definitions are only descriptions of what is actually happening. Man (or woman) walking over a trail. How much weight does he carry? Wheeling a canoe means half the weight of the canoe, the other half is on the wheels. Do you add the entire weight, or only half? All are imprecise as far as they go, never absolute...till you are actually walking on the trail, they are only words and only used for comparison. FSO, Base weight, Pack weight are only words. Everyone will have their choice measurement. To a new hiker, understanding them all is what IS important.