I understand the purpose of the founders in setting up a legislative body that would not be so swayed by popular sentiment- part of that whole “republic” thing, but still…..

That wasn't really it, actually.

When the country was founded, States were much more like countries. Not just in the Articles - even under the Constitution, States were (and are) still very much sovereign entities, with vast swathes of governmental power reserved solely and exclusively to the States. Almost all regulation was made by State legislatures, not the federal government.

Which is why the Senate looks the way it does. It's like in the EU - while the EU Commission has been delegated a sizable amount of power, the countries that make up the EU are still very much countries. People are very much citizens of the country they live in and the EU, and the EU isn't set up so that citizens from different countries are just amalgamated in a single popular vote. Countries have a voice in the EU that is based on their status as countries, not just based on their population.