There's no evidence that the Electoral College had anything to do with Slavery. The founding fathers specifically did not want a nationwide vote of the American people to choose their President.
Instead, they gave a small group of people called the “electors” the power to make that choice. These would be upstanding citizens chosen by the various states, who would make up their own minds on who should be the president.
It gave some extra power to smaller states in that each state get 3 electors even if their population is tiny.
"Some argue that the Electoral College ensures regional balance, since it’s mathematically impossible for a candidate with overwhelming support from just one or two regions to be elected.
But when we get down to brass tacks, the most serious objections to reforming the Electoral College come from rural and small-state elites who fear that under a national popular vote system, they’d be ignored and elections would be decided by people who live in cities.
Gary Gregg of the University of Louisville wrote in 2012 that eliminating the Electoral College would lead to “dire consequences.” Specifically, he feared that elections would “strongly tilt” in favor of “candidates who can win huge electoral margins in the country’s major metropolitan areas.” He continued:
If the United States does away with the Electoral College, future presidential elections will go to candidates and parties willing to cater to urban voters and skew the nation’s policies toward big-city interests. Small-town issues and rural values will no longer be their concern."