I'm going to regret engaging with you, but A) Slate does not dictate the opinions of an entire faction of the country. B) Obviously, Slate employs a wide range of contributors who, it would seem, disagree with each other.
But to reiterate A, even if you found two articles written by the exact same person that flip-flopped in this manner, the Electoral College and indeed electoral practices in general have been criticized non-stop for a long time. The closest it ever came to being repealed was under Nixon, of all people.