I was not being reductive.
Money gets to vote on candidates before people do. Before any general election there is a primary, and to win the primary you do fundraising. People with money give politicians money with the implicit understanding that making anti-donor decisions will result in withdrawal of future money or (thanks to citizens united) unlimited contributions to their opponent.
Money literally votes on political candidates before any person does. That is why we have a "democracy" more responsive to money than to the will of the average voter.
Even if you look at it as a black box, Princeton did a study and asked if the legislation our politicians pass correlate most with the average citizen, interest groups, or the desires of rich people, the correlation was highest with rich people: https://scholar.princeton.edu/sites/default/files/mgilens/fi...
Multivariate analysis indicates that economic elites and organized
groups representing business interests have substantial independent
impacts on U.S. government policy, while average citizens and
mass-based interest groups have little or no independent influence.
Here you can watch Harvard Law professor Lawrence Lessig talk about this issue:
https://www.youtube.com/watch?v=PJy8vTu66tEAs wealth concentrates, it is able to purchase and corrupt further institutions. Bezos bought WaPo, Musk bought Twitter, I'm sure there are more examples. Do you think that is a form of power that is able to manipulate public opinion or government policy? Do you think ownership of a media outlet could help a person concentrate their wealth or fight being taxed?
Even from a mathematical approach. If Billionaires are able to earn 5% year over year interest at minimal risk, while large swathes of people will never make enough to have a savings, what do you think the long term consequences of that will be? If inequality is increasing and never decreasing, what do you think the long term effects will be? What types of things cause inequality to decrease, are we doing those things?
How much wealth has to concentrate before you are comfortable labeling it oligarchy?
Here is Yale history professor and expert in European history Timothy Snyder talking about oligarchy, the rule of the wealthy few. "What is oligarchy?": https://www.youtube.com/watch?v=biZVrh821RA
In this video he explores what oligarchy is and what effect oligarchy (the state of extreme wealth inequality -- too many billionaires) has on social programs like healthcare, namely that there won't be social programs/investment in institutions.