From his best bio (The Outlier) to thd Fresh Air retrospective and the American Experience documentary, my conclusion is that he was underrated as a President, and overrated as a politician.
Yes, he was a major underdog who won the Presidency, but Gerald Ford had Nixon’s legacy and bumbling persona while Ted Kennedy’s personal demons did him in, presenting Carter a gift. Carter was America’s reactionary vote against the grift and dishonesty of Nixon. Perfect timing for a fighter of grift like he was (see his takedown of rural Georgia political bosses). He also made horrible political calculations because of his humanity: after the high of his popularity in ‘78 and the Camp David Accords, he went on foreign relations quests around the globe while the inflation and oil embargo crushed Americans here. He abandoned his strongest allies in cutting poverty programs first in his austerity budget. And he accepted the Shah in America to get treatment for cancer when it inflamed the Iranian Revolutionaries. Their waiting until after the election and inauguration ceremony of Reagan was their middle finger (though now we know Reagan and his people actively lobbied for Americans to be held there, and we know all about his “arms for hostages” position).
But he got a lot of consequential legislation passed. The budget deficit was down and employment was up by the end of his presidency. He increased government efficiency by deregulating cargo on trucking and flights. Yet he did increase social services, expanded national parklands, and signed significant environmental regulations into law.