I basically agree.

I think it is tied to the expectation of fairness and the perception of fairness.

If you expect to get the same bonus, and you perceive you were slighted, you will probably be unhappy.

Perspective plays a huge part.

That's not to say people don't have valid grievances, but there is a huge amount of cognitive dissonance, and large gaps between expectations and reality.

Take the parent example of US inequality. Low earners are unhappy that they make so much less than US high earners. Well that's unfair! However, they certainly don't gain much comfort by being a high earner globally. That's not unfair, that is deserved!

As your example perfectly illustrates, our perception of fairness is extremely biased, and therefore is not a good metric.

"Compare yourself to who you were yesterday, not to someone else today"

Our perception of fairness is parochial, so it's biased against the outgroup, but it works very well within the ingroup. But in- and outgroup are not rigidly defined and can be changed. If you maximize the size of the ingroup, there's nothing wrong with innate farness.