Once you actually read it then you'll find out that it does:
> What do our findings say about democracy in America? They certainly constitute troubling news for advocates of “populistic” democracy, who want governments to respond primarily or exclusively to the policy preferences of their citizens. In the United States, our findings indicate, the majority does not rule—at least not in the causal sense of actually determining policy outcomes. When a majority of citizens disagrees with economic elites or with organized interests, they generally lose. Moreover, because of the strong status quo bias built into the U.S. political system, even when fairly large majorities of Americans favor policy change, they generally do not get it.
The study literally concludes that regardless of what party is in power, it's the interests of the oligarchs that take precedence. Whenever there is a difference of the opinion between the masses and the oligarchs then the oligarchs typically win. That's whose interests the parties represent.
And, if you think that's what a democracy is then what else is there to tell you.
You claimed that both parties represent the exact same interests, and I don't agree with that at all and nor does the article support it.
If we use campaign contributions as a proxy for interests, then internet companies like Google and Facebook and their employees support Democrats much more than they support Republicans, and it's vice versa in the aerospace and defence industry.
Once again, both parties represent the interests of the ruling class in American society which is the capital owning class. This is precisely what the study shows. This has absolutely nothing to do with democrats or republicans. The division in American society is between people whose primary source of income is their capital and those whose primary source of income is their labour.
There's no monolithic "ruling class" that both major parties serve equally, and nor did the article claim anything like that. Instead, there is a huge patchwork of constantly shifting interest groups who are looking for suitable candidates to support, and candidates who are tweaking their platforms to appeal to as many groups as possible. Why would, for example, Fortune 500 companies spend a dime on elections if both parties served them the same.
The idea of a singular ruling class controlling the whole country is a lazy conspiracy theory that ignores the complexity of politics and governance.
> What do our findings say about democracy in America? They certainly constitute troubling news for advocates of “populistic” democracy, who want governments to respond primarily or exclusively to the policy preferences of their citizens. In the United States, our findings indicate, the majority does not rule—at least not in the causal sense of actually determining policy outcomes. When a majority of citizens disagrees with economic elites or with organized interests, they generally lose. Moreover, because of the strong status quo bias built into the U.S. political system, even when fairly large majorities of Americans favor policy change, they generally do not get it.