Here is some data that compares the median income to the rising cost of living in the US. https://www.businessinsider.com/america-middle-class-living-...
I think the Bezos-Ferrari question is a good one. I feel it is personally unethical for Bezos to spend that amount of wealth on luxuries when the resources could alternatively be spent reducing the suffering of others.
However I also think it is impractical and misguided for a state to enact policies with the primary purpose of minimizing the number of Bezos Ferraris or to automatically attribute the lack of cars per capital to Bezos's excess of cars (although in some cases it might be)
I admit it's a difficult thing to measure and to discuss, but I also do think that the tide is rising, but being creatures who's feel good brain chemicals are related to relative outcomes (see the primates w/ cucumber vs grapes studies), we're also feeling a bad feeling because we see others doing better to a greater extent than we are...
To talk about the difficulties of implementing true socialism would be beating a dead horse, I think. But even if we could remove wealth inequality completely, people would still find ways to feel better or worse than others (sports, looks, social skills, intelligence, etc.). My high school in the suburbs was fairly homogenous from a socioeconomic standpoint, but that microcosm seemed more hierarchical than any other point in life.
I also would expect the good-or-bad feelings people get by making comparisons are more-or-less ordinal in nature, so I think people would manage to feel just as bad about small wealth differences (keeping up with the Jones's) if there were no more billionaires.
The main one that jumps out for me is power, and influence. As an example, it doesn't really matter if I can donate $100 to the EFF instead of $50 when a billionaire can outspend me 1,000,000:1 without even flinching.
I found this interesting on the topic: https://www.forwardparty.com/democracy-dollars
Do you define regression as absolute position or relative position? For example does it matter if Jeff Bezos has 100 Ferraris if the middle class, on average, have .25 more cars per capital than 50 yrs ago?
I would love to put some data behind this discussion because it's long been mixed up as to which case is the ethical one (absolute vs relative growth).