The Electoral College did give the slave states more power, by way of the three-fifths compromise: the number of Electors depends on the number of Representatives, which depends on the census of inhabitants, not vote-eligible citizens, including, at the time, 3/5 of the slave population. So a state like Virginia, with more slaves than free people, got a boost compared to a state with only free residents.
The Electoral College did give the slave states more power, by way of the three-fifths compromise: the number of Electors depends on the number of Representatives, which depends on the census of inhabitants, not vote-eligible citizens, including, at the time, 3/5 of the slave population. So a state like Virginia, with more slaves than free people, got a boost compared to a state with only free residents.