HEDGE-FUND managers may be feeling quietly smug about their performance in 2017. They returned 6.5% on average, according to Hedge Fund Research, a data provider, their best year since 2013.But those returns do not really suggest that they are masters of the investing universe. The S&P 500 index, America’s main equity benchmark, returned 21.8%, including dividends, last year. More tellingly, a portfolio split 60-40 between the S&P 500 and a mixture of government and corporate bonds (an oft-used benchmark for institutional portfolios) would have returned 14.8%.