Yeah I agree with you that once you get to a high level like that, you need more money to maintain. I do disagree that there is no amount of money easily attainable by the middle class that would earn passive income sufficiently however. If we look at average annual returns on the stock market over long periods of time, if you are saving the right amount from when you are 24 or 25 you can live off your dividends by the time you get to around 55-60. High dividend yielding mutual funds/etfs can get you around 2-3% dividends a year, but the key is to live below your means.
Like you mentioned in the first part, the mansion and the large properties becomes a trap. Why do we need a 12 bedroom house for a family of 4? If people live frugally they could easily live their lives and pursue their passions without having to work, or at least not having to work a 9-5 job. Billions of dollars is a different story, you have to get much more creative there, but if your net worth is under 50 million you can still use the stock market without pushing prices much. There are relatively low risk options like VDC, a consumer staples etf which has a dividend yield of 2.16% and almost always goes up because consumer prices are always increasing. There are many lower risk options out there that can help you maintain your lifestyle without having to work a 9-5.
I do agree however that now in the current way things are looking, everything could change. Negative interest rates are essentially a money tax and taxes in general do greatly affect how well you can live off your salary.