What was heartland rock? Did anyone ever really know? No less an authority than John Mellencamp dismissed the term as the work of “lazy journalists.” But in the 1980s, the music’s heyday, the phrase denoted an array of artists and tendencies while also conjuring something more atmospheric. Everything about the sound was big: the guitars, the drums, the voices, the choruses tailor-made to be shouted along to at a stadium or at a wedding or in your car, nowadays probably to the embarrassment of