The founders were reluctant to use any system other than ‘Congress picks the president’

Exactly, and the compromise they eventually settled on was “state legislatures collectively pick the president.”

The idea of Electors was simply a result of that, as a workaround for the fact that “one state legislator, one vote” wouldn’t work because different states had them representing different numbers of constituents.

It was not initially intended for Electors to be chosen by popular vote.