An important element of the conversation is does (or how much does) it matter if any specific percentile group is getting disproportionally richer, given all (or a vast majority of) groups are? A group's lack of upward movement is not unjust if their groups actions do not justify a movement upward.
Additionally we also have to recall that the quintile's populations are not necessarily static. to illustrate the idea: members of a quintile may join an adjacent quintile in the next time period. That is, bottom members may move up, top members may move down, mid members may move either way. To the extent their movements are justified by their actions/choices is to the extent we have a fair society.
That is, if people are getting rich from sources not related to taking right actions, or people are taking good actions and getting poorer -- then we have an unjust society.
This can both apply to Rich people abusing their power to get rich, but also with poor people abusing their democratic powers to unjustly take from others that which they have not earned.
Additionally we also have to recall that the quintile's populations are not necessarily static. to illustrate the idea: members of a quintile may join an adjacent quintile in the next time period. That is, bottom members may move up, top members may move down, mid members may move either way. To the extent their movements are justified by their actions/choices is to the extent we have a fair society.
That is, if people are getting rich from sources not related to taking right actions, or people are taking good actions and getting poorer -- then we have an unjust society.
This can both apply to Rich people abusing their power to get rich, but also with poor people abusing their democratic powers to unjustly take from others that which they have not earned.