Here's is your claim:
Trump started with about $100 million in 1968. That’s about $671 million in today’s dollars.
During the 20th century the stock market returned an average of 10.4% a year. We’ve accounted for inflation above, so investing $671 million over 45 years at 10.4%/year gets you to $57 billion.
You can't inflate the 1968 dollars and then magically put that amount into the stock market and base your expected growth off that. Simply not possible.
When you put $1 into the market, and the market doubles, you end up with $2. If inflation cuts the value of that dollar in half you still have the $2, even though it now only buys as much as your original $1. If deflation were to make the dollar double in value, you would still have $2 based on the investment above, but it would have the spending power of $4 compared to the original $1. It doesn't change whether the dollar is worth more or less.
Bottom line: Your "math" is seriously flawed. You can't take the original investment number and apply potential inflation to it to get your original investment amount.
All right then, calc it out yourself and use whatever deflator you think is appropriate. Either way he didn’t out perform a broad market index. That index is the normal way to judge if a money manager is good or bad. If they hit past it, then they’re good. If they don’t, then they’re not.
Soros, Koch and Buffet hit past it. Romney and Trump don’t. Both Romney and Trump told us they’re great businessmen hire us to run the country.
No thanks.