Features of the United States political system that violate the one-person-one-vote principle:
Features that are less cut-and-dry, but nonetheless result in political decision-making being unrepresentative of the will of the people:
I am aware that some of the founding fathers supported various "counter-majoritarian" aspects of law. However, straying from one-person-one-vote means that you have chosen a dominant minority to rule over you. It matters less who you chose to be the dominant minority, what matters is that you have chosen some dominant minority to rule over you, and that's a real problem.
I agree with Winston Churchill who said "Democracy is the worst form of government – except for all the others that have been tried". Democracy is definitely not perfect, but we haven't managed to find a proper benevolent dictator yet, so I don't know what other option we have.