Vague? It's pretty concrete. You may make a perfectly logical business-related argument as to why this compensation difference is acceptable, but why would that have any effect on the obvious, intuitive perception that it's unfair from the point of view of a rational human?

Businesses do inequitable-by-definition things all the time. It's part of their DNA. They make measured trades, and often those trades involve mistreating humans, betting that the practical consequences of that will be worth whatever the upside of the trade is. That's why we have so many laws and organizations protecting people from businesses.