The Electoral College is not a vestige of slavery. It is a vestige of the world's first experiment with the new type of government known as federalism. The electors were nothing more than the interface between the national (federal) government and each of the state governments. Seats for electors were apportioned to states, and it was up to the states to figure out who to send and how they should vote. It is certainly true that the apportionment of the number of seats was in accordance with "The Three-fifths Compromise," to appease slave states, but the Fourteenth Amendment ended it.

The problem people have with the Electoral College is that all states but two award all their electoral votes to the winner in each state. If states awarded electoral votes proportionally, the Electoral College result would match the popular vote closely. Support the National Popular Vote Interstate Compact to fix the problem.

https://en.wikipedia.org/wiki/National_Popular_Vote_Interstate_Compact