Only a few years after his death, when I started listening to country music, it was called country or country & western. "Hillbilly" was already a politically incorrect term. Like the N-word today, it can only be used reflexively, like Kenny Chesney calling himself a hillbilly rock star. As a musician and specifically a bassist, to me it's just the rhythm. Hank Williams's faster tunes like "Hey Good Lookin'" and "Half as Much" have a textbook swing beat. Sure, he didn't have a complete dance band with woodwinds like Hank Thompson, but those fiddle and pedal steel solos really swung. A swing beat is simply a highly syncopated twelve-beat, which practically every C&W hit song had in the 1950s. Western swing, in addition, had a light backbeat that was picked up and accentuated by rockabilly and ultimately rock and roll. I think his arrangements made up for that with the backbeat. That draws people onto the dance floor regardless of the lyrics. I thought that was already a signature technique in bluegrass, and before that the Celtic fiddling it evolved from? I admit I'm not familiar with the early bluegrass songs but the fiddlers were all double-stopping by 1957.