While an S&P 500 index fund is clearly a better alternative to the vast majority of stock-picking strategies and funds, it can also decline and even crash right with the market...because it IS the market!
In 2007-09, the S&P 500 lost 56% in 15 months and took 6 years to recover!
In 2020: "The global economy is heading for its worst year since the financial crisis."
... Bank of America
February 27, 2020
The ideal strategy would be one which could capture the S&P's gains in good years, but avoid the declines in the bad years. Actually, it's easy to do.
You do it by "insuring" your position in the S&P at a nominal cost, then recovering that cost during the year. Result: If the market goes up, you capture that appreciation. If the market goes down, you lose nothing...because you had the insurance!
Right now, you could buy 1 year's worth of insurance on a $300,000 investment in the S&P 500 for a net cost of around $12,000. Then, during the year, you will execute a few simple option transactions...requiring no additional investment...which will raise cash to recover most if not all of the $12,000.
At the end of 12-months, you will have either captured most or all of any S&P 500 gains on $300,000 for the period, or lost little or nothing if the market declined or even crashed!
Virtually no other stock-picking strategy...or index fund...can promise that result!