Spokes just about never fail through overload, unless you get something caught in the wheel.


So "stronger" isn't the characteristic people are after.
Spokes generally fail by (metal) fatigue, similar to bending a paper clip at the same spot repeatedly.
The characteristic people are after when building with different gauges is endurance, resistance to fatigue.
If you match the differences in cross-section area to the differences in DS/NDS tension, the elbow of the NDS spoke will experience less flex and be less prone to fatigue failure.


The thing to remember here is that sometimes there's very little actual gain by going from "good enough" to "better".


If your wheels stay true and spokes hold up using straight-gauge spokes, the only benefit from thinner NDS spokes is a tiny weight reduction.
Perhaps an even tinier aerodynamics improvement.


And since straight gauge spokes are cheaper and easier/faster to build with, you might as well stick with them unless there's an actual problem you're trying to fix.