This is, of course, a tautology. History, the only arbiter of truth, reminds us that when someone rises up and ousts the rich and powerful elite, their next step is to make themselves the rich and powerful elite.The US is dominated by a rich and powerful elite.
Sure. Although history has its own arbiters. Which coincidentally doesn't include those so poor and powerless that their version is not heard. Our modern version of democratic states is supposed to curb the relationship between wealth and influence on political decision making. Showing empirically that the system is a functional plutocracy implies a serious lack of political legitimization in any narrative which is still formally democratic. It's true that in a well developed plutocracy like ours, removing one group of plutocrats only replaces them with another group, which was your original point. Yet the mainstream consensus as suggested by mainstream media still implies the existence of a functional (not just formal) democracy. That makes the findings discussed here quite relevant to every informed political discourse.