I think that James Simons is an example of someone with an unusually strong comparative advantage at making money. But this wouldn't necessarily have been clear a priori: if you put yourself in Simons' shoes in 1980 the expected earnings of going into finance would be much lower than his actual earnings turned out to be. So it's not clear that he would have done better to "earn to give" than doing something of direct humanitarian value (though maybe it was clear from the outset that his comparative advantage was in finance.)