The founders were literate and routinely wrote down their thoughts (see citations at the bottom of wikipedia).
https://en.wikipedia.org/wiki/History_of_the_United_States_S... https://en.wikipedia.org/wiki/History_of_the_United_States_C... https://en.wikipedia.org/wiki/Connecticut_Compromise
Consider that in Canada's House of Parliament, we similarly have votes in rural areas overrepresented compared to their urban counterparts. Did that system arise from slavery as well? Of course it didn't, and any Canadian suggesting so would be laughed at.
Can you explain why? I probably have a childlike understanding of the histories of Parliament and slavery in Canada.
The reality is that the early US was a lot more similar to a federation of independent states at its birth than today. A senate ensured the spirit of a federation would be kept.
This book definitely agrees with GP and disagrees with you. You might want to check it out.
[1] https://www.whitehouse.gov/about-the-white-house/our-governm....
[2] https://law.marquette.edu/facultyblog/2012/12/before-there-w....
Here's the 1802 house just to drive the point home. I suggest sorting by the "seats" column
https://en.wikipedia.org/wiki/1802_and_1803_United_States_Ho...