Hard work may give you an edge over other people in the same job role, so seniority way be seen as somewhat correlated with hard work within a position, but across job roles pay is much more dependent on other factors for instance the opportunities provided to you by your wealth, race and sex to name a few. I'm of the opinion that just because someone is paid less, doesn't mean they work less hard, and I don't think it fair to begrudge people their pay for quite possibly just not being born with the same silver spoon.

P.S: Not to imply that wealth, race, and sex don't also hinder you within a job role, but I think that it's probably even more prevalent across them.