I am sure if what we just read in the Gospel took place today, there would be a huge hue and cry. For us justice has a very definite sense of equality. Salaries are linked to hours of work. A skilled worker gets more than an unskilled worker. If workers have the same skills, the same hours of work and similar responsibilities, we expect them to get the same wages.
Equality is justice and justice is equality.
This is our way of reasoning. Therefore, this parable does sound strange to our ears. However, if we read this Parable carefully, we notice that it is not talking about wages and justice. For such an interpretation, too many details are lacking. We are not told anything about the salary that was agreed upon.