There is a business-class only airline (La Compagnie) that flies from Newark to Europe and they're profitable. A little more expensive than 2x the price though, but less than 10x.
Never heard of this airline so I just checked: Over the next few months the cheapest flight from EWR to their base in Orly is ~$2,500 vs ~$365 for Economy (French Bee to be exact). That seems like its still a separate class and would exclude most Economy flyers.
https://en.wikipedia.org/wiki/La_Compagnie