That is good. It certainly is not unjust. So the question why does it seem so. Modern Catholic Dictionary has under
Justice: “As a virtue, it is the constant and permanent determination to give everyone his or her rightful due. It is a habitual inclination of the will and therefore always recognizes each one’s rights, under any and all circumstances.”
Matthew 20:
4 and he said to them, ‘You too go into my vineyard, and I will give you what is just.’
So if it is unsettling then there is the idea that one has a right to what is given. But in the example what is paid is what the person has a right to, and any excess is a gift not a right. The teaching of the parable is about the saving grace (a gift) for which more is needed for some but not for others. In considering what actually happens, the Beatific Vision of those with more merit is greater than those with less, however, merit is acquired through willful good actions after being in a state of sanctifying grace.
Note some dogmas of faith (from Fundamentals of Catholic Dogma):
Grace cannot be merited by natural works either de condigno or de congruo . (p. 236)
The degree of justifying grace is not identical in all the just. (p. 262)