What kind of stress do you mean that single piece type straps exerts on attachment bars/pins? I can think that the direction is more downwards with this type of straps than the more regular sideways stress that 2 pieces straps exert. I can imagine that a single piece strap that's too thick to be fitted can cause additional unnecessary pressure on the bars.
The direction of the force makes no difference. The effect on the springbar is the same wether it is pulled down or outwards.
The way the G10 is designed, with one end ´floating´ on the strap itself the pull is mainly on óne bar whereas with a normal 2-piece strap the force would be devided over both.
There should be no marked difference with a simple non G10/Nato pull-through strap.
Indeed a thicker pull-through strap put more stress on the bar unlike a thicker 2-piece band in which case it has no effect.
This noted it should be observed that good quality springbars are pretty strong and should give little problems. Cheap ones should be avoided.
Also the springbar ends seat better in drilled through lug holes and are thus more resistant.
Yes, the nylon strands pulling at the shoulder are an issue. I did not mention is as the topic was about leather.