according to the test Larry H did, the hard and neutral axle deflected the same amount, under the same load
Are you saying he should’ve ran the test with a much heavier load?
the AMV chart list the different yield index of axles, stiffer being higher yield index, my understanding is yield index is the point where steel tubing begin to deform permanently, and tensile strength is where it breaks.
If this is correct, then normal kart driving should never reach even the yield index.
It would be interesting to see a chart of the deflection curve of the different axles up until the yield index limit.