So part of the issue with etched running boards is a limitation of the process.
Current etched running boards are indeed too thin, compared to the prototype. When designing an etched running board, the grid cannot be thinner than the thickness of the sheet material. So if you desire the lacy look of an Apex design you have to sacrifice thickness.
Some people have tried to deal with this by designing a running board that is 2 pieces and you fold over onto itself. The new S scale CNR 8 hatch reefers use this approach.
Experiments are underway right now to try a slightly different approach to the design process and get correct thickness running boards. Stay tuned.
Typical white or yellow brass is far too soft for this application. Stainless steel or nickel silver has been used for it's resistance to kinking and Phosphor bronze is also a good choice.
Having said all that, for a metal running board I prefer a too thin item over a too thick item. Just my opinion.
Pierre Oliver