The biggest mass on the bike is the rider and if you start hanging heavy stuff on the bike a long way from the rider then the farther away from the rider and the heavier it is the greater the change to the way the bike handles. If you can get that mass very close to the rider then it's almost like the rider just being a bit heavier, at least when in the saddle. Putting heavy stuff low down makes the bike fee sluggish, but it's stable and that was always the touring norm because weights and volume could be quite large and any practical solution meant that bike handling had to be sacrificed. But with lightweight bikepacking type setups (which I know you were using well before the current fad for them) it's possible to reduce weight and volume so that you don't lose all the feel of a bike.


As to your point about young tourers carrying a lot of stuff and older ones going lighter I think the explanation is experience. If you've toured a few times you realize that the pain of carrying useless stuff is not worth it. I remember a young touring couple blog about their gear list and they included a paella pan which was quickly sent back.