Let's be clear.
Your reference is Mother Jones. It's light-hearted journalism. As to the Donald's wealth, here's exactly what your reference said:
Donald Trump Has Lost Between $1 and $6 Billion Over His Business Career | Mother Jones
Over at National Journal, Shirish Dáte estimates that if Trump had put that money into an index fund of S&P 500 stocks, it would be worth about $3 billion today.
Now, The Donald filed paperwork claiming his net worth at $10 billion. Forbes currently estimates his net worth at $4.5 million. He claims it's $10 million. By all accounts the Donald has done better than the S&P index funds.
You mean after he'd already increased his net worth from $40 million to $200 million in a few short years. That's kinda cherry picking a data point if ever there was one.
Also, about that S&P500 index he should have invested in ... it didn't happen until after 1974.
S&P 500: A Great 2nd Place Index Fund | Forbes
The S&P 500 has the distinction of being the first index to be tracked by a publicly available index fund. The Vanguard 500 Index Fund (ticker: VFINX) began operations on August 31, 1976.
Like a lot of other stock market picks which look wonderful in hindsight, the S&P500 just happens to be the index which is in vogue now. If the Donald had managed to invest his entire net worth in S&P500 index in 1976 when it opened he'd have been an oracle as well ... for knowing which of the myriad of stock market indexes was going to do well. It could have been the Dow100 or the Dow30 or one of the lesser known indexes.
Regardless, despite the misleading Mother Jones headline, the Donald has clearly outperformed even the currently favored S&P500.