Instead, the states would each appoint independent electors who would cast the actual ballots for the presidency.

In other words, like having Congress do it, but with added Federalism by giving it to the state legislatures instead of the federal one.

The “Electors as intermediaries” part was wasn’t directly about reducing corruption, because having the state legislators choose would’ve already solved that. The only trouble was that “one state legislator, one vote” wouldn’t work because different states set up their legislatures differently and with varying numbers of constituents per legislator, so they needed a sort of ‘compatibility layer’ to compensate for those differences and the solution was having state legislatures appoint Electors.