These matters are all VERY complicated. As you have suggested, it really isn't right to compare the cost of steel on an adjusted exchange rate. This is true for everything, not just steel.
Other factors include income, taxes, subsidies, cost of living, quality of life, etc etc.
One very reasonable way to compare such things is to look at what we call disposable income. Disposable income is how much money you have left over after all other bills and taxes have been paid. In other words, how much is left to buy toys or vacations or other luxuries.
On this basis, people living in the USA used to be twice as wealthy as Canadians because they had twice as much left over. It used to be that Canadians had about double the disposable income as people living in China. But I don't know what those numbers are today.
It's easy to compare raw costs of metal, but that ignores affordability. It also ignores government policies which are usually designed to improve international competitivity. These policies can have a huge affect on the cost of certain products and materials.
