S&P 500 investors are betting on a handful of stocks like Tesla and Nvidia, Apollo's Marc Rowan warns

• The S&P 500 is dominated by a handful of Big Tech companies like Apple and Amazon.
• Investors in the index are speculating on just a few companies, Apollo's Marc Rowan says.
• Rowan says it's a tougher backdrop today, echoing one of his key influences, Warren Buffett.

The S&P 500 has become so concentrated that investors are basically betting on a handful of mega-cap stocks like Tesla and Nvidia, Marc Rowan has warned.

"I don't even know if we have a stock market anymore – 10 stocks are like 35% of the US S&P 500, and 80% of volume is in the S&P 500," he told The Australian Financial Review in a recent interview.