Management expert Jeffrey Sonnenfeld is going after activists investors—saying Thursday ordinary investors would do better putting their money into the stocks of the target companies than the investment firms on the attack.
Activists "should be held to the same accountability that their target firms are under," the Yale School of Management senior associate dean told CNBC—echoing a position he took in a Wall Street Journal op-ed.
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In a "Squawk Box" interview, Sonnenfeld singled out Nelson Peltz's Trian Fund: "Last year ... Trian came in at 8.8 percent return. The S&P was 13.7 percent."
"That's just the facts," he said.
Trian defended itself in a statement to CNBC:
"Mr. Sonnenfeld has twisted and cherry-picked the data to present a highly misleading and inaccurate picture of Trian's performance. The fact is that Trian has delivered excellent results for our investors, which is why we have $12 billion in AUM [assets under management]. Our flagship fund has generated a 137 percent return net of fees since inception in November 2005, outpacing the S&P 500 by 2,900 bps [basis points]. And if you look at our core positions from the day we invested until today, we have outperformed the S&P 500 by an average of 764 bps annually. That outperformance increases to 879 bps for companies on which Nelson Peltz served on the board."
Sonnenfeld responded to Trian's statement, insisting that Trian is "underperforming their own target companies" such as DuPont, the chemcial company locked in a proxy war with Peltz.
"If you put $100 in DuPont when Ellen Kullman became CEO [in 2009], that would be worth $240 today," according to Sonnenfeld's calculations.
"If you put it into the S&P 500, it would be about $200," he continued. "If you put it into Trian, it would be worth $190."
Trian has proposed adding Peltz and another nominee to DuPont's board as well as two other nominees to the board of a unit DuPont plans to spin off.
DuPont is planning to spin off its performance chemicals business, but Peltz wants the company to separate its nutrition and health, agriculture and industrial biosciences divisions from its volatile but cash flow-strong materials businesses.
DuPont has rejected the proposal, stressing that keeping its businesses together would allow the company to benefit from its science platform, global scale, market access and brand.
In a CNBC interview in March, Peltz said breaking up the company would be "the most efficient way" to get rid of $2 billion to $4 billion in costs.
The company's shares have risen nearly 9 percent since Trian went public with its break-up proposal in September.
"This is a huge sea change. If we were having this discussion ... 25 years ago we have many of the same people [like Peltz]. They were called sharks, raiders ... at that time," Sonnenfeld argued.
—CNBC's Maneet Ahuja and Reuters contributed to this report.