The idea that the country is deleveraging — reducing its debt — is a myth, says Russ Koesterich, chief investment strategist for BlackRock.

"Like all myths, there is a kernel of truth," he writes on the firm's website. "The U.S. financial system has indeed made significant strides in reducing leverage, and U.S. banks are better capitalized."

But when it comes to the economy as a whole, "there has been no deleveraging. In fact, as revealed most in the latest revised GDP figures, we’ve generally seen quite the opposite," Koesterich says.

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For instance, he notes, U.S. household debt stands at 103 percent of disposable income. As for corporate debt, during the last six quarters, it has climbed at an average annualized rate of 9.5 percent. "Meanwhile, federal government debt has exploded," Koesterich writes.

Overall, "during the period of so-called deleveraging, non-financial debt has increased by roughly $9 trillion."

The long-term implications for the economy: "slower growth, a persistent headwind for consumers and vulnerability to even a modest rise in interest rates," he notes.

"Over the longer term, a high and growing debt burden has several implications for the U.S. economy: slower growth, a persistent headwind for consumers and vulnerability to even a modest rise in interest rates (this is particularly true for the federal government, where an improving fiscal picture has been flattered by artificially low rates)," Koesterich explains.

"In fact, the rising U.S. debt burden is one of the reasons why I continue to advise caution toward consumer sectors as well as why I have more modest expectations for long-term U.S. stock returns."

Meanwhile, Larry Summers, former economic adviser to President Obama, says the U.S. economy has suffered major flaws that date back even prior to the 2007-09 recession.

"It has been a long time since the American economy has grown rapidly in a financially sustainable way," the Harvard professor tells New Republic magazine.

The Federal Reserve's low interest-rate policy hasn't been able to solve the problem of savings exceeding investment, he says.

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