As an American, I can say that what OP is saying is not at all how the parties function, but it is maybe what most Americans think. I think, the real answer is

As an American, I can say that what OP is saying is not at all how the parties function, but it is maybe what most Americans think. I think, the real answer is that both parties rule for the oligarchs, just different ones, and they also take on opposing sides in certain culture wars that Americans care about to win votes.