IMHO I would perfer a low scar diameter "oil" over a higher one BUT if the difference is only 5-7% I would call both oils even.
That said in a IC engine the closest you can get to a 4 ball test regime would be the cam lifter noise and cam drive gear.
Bye the way the most common test for a 4 ball rig is EP gear oil.
So the test as related to a IC is OK but not a big deal I would perfer a Camshaft lobe wear test of which ASTM has one.
I suspect Amsoil happens to have a 4 ball test machine and has decided to use it, I do not blame them but it just does not apply to well.