There’s a huge difference between 300% inflation the BLS claims vs. 2800% inflation you are suggesting.
On a practical level, inflation is always relative to what you're actually buying. If you're buying S&P 500 index funds, the inflation rate is the price appreciation of the S&P 500. If you're buying real-estate, the inflation rate is the rate of increase in housing prices.
(Perhaps this is a bad example because you typically wouldn't be buying stock index funds after 40 years of earning, but the point is to illustrate opportunity cost. If someone's goal is to pass wealth on to their children, for example, then the price of income-producing assets is a lot more relevant than the price of milk.)
The price of goods, services, salaries, etc. have all gone up by roughly 3–4x in the US (with some notable exceptions like housing in certain areas and college tuition). Someone who invested in the S&P 500 and has 29x as many nominal dollars as they did in 1976 can buy about 8 times as much of other people’s labor as they could before.
Some fixed percentage of the total size of the S&P 500 is a practically useless measuring stick. If we use that as a standard, 90%+ of the population in the USA is 8x poorer than they were in 1976.