I agree that republican democracy is favorable to direct democracy, in that it frees the average citizen of the need to be well-versed and well-informed regarding numerous matters of civic interest.

But we shouldn't conflate this justification with the side effect of having disproportionate representation for different segments of the population. Yes, to some extent this will happen in a republic, and the Senate was indeed constructed as it was so that the interests of smaller states would not be overwhelmed by those of larger states. Yet I'm not sure the founders envisioned a 70-to-1 ratio between the populations of the largest and smallest states. Furthermore, they envisioned the Senate being more "detached" from the ear-to-the-ground politics of the House (hence the six year terms). The Senate was to be the more distinguished and "deliberative" body, and one more inclined to put politics aside when appropriate. They hoped that political parties would not come to dominate the Senate, and that it would value its own institutional authority and prerogatives over shared political goals with the executive. That is why they were given the task of advice and consent to Supreme Court nominees (and conducting impeachment trials). Needless to say, while at times the Senate has approached this ideal, it is far from it today.