Vanguard Group Founder Jack Bogle expects a moderate-to-serious recession lasting at least a year-and-a-half, or longer.

Even so, Bogle feels that the market has priced that recession in by now.

Meanwhile, the fundamentals of the U.S. stock market have “improved radically,” Bogle says. “Declines in valuations are overblown."

“The value of the U.S. stock market was $18 trillion a year ago. And now it's about $9.5 trillion or let's call it $10 trillion with today's rally,” he told CNBC, referring to the pre-election run in which the S&P 500 crossed the 1,000 mark for the first time since Oct. 13.

Since sold off, that day the three major U.S. stock indexes ended up around 18 percent from their closing low points on Oct. 27.

"Anyone who believes that American business is worth $9 trillion less than it was a year ago, I think, is a fool," Bogle says.

"We now have a higher dividend yield of 3 percent compared to 1 percent a few years ago. Earnings growth will be faster than the economy from these depressed levels, and with the market-to-book value ratio, the market is selling about 1.8 times book value.”

“I don't think it's done that since 1985," Bogle says.

Leuthold Group CEO Steve Leuthold sees stocks as undervalued as well.

The intrinsic value of stocks is the most positive since 1984, Leuthold told Barron’s.

"On a valuation basis, this is a really cheap market," he notes.

“From here, on a one-year basis, and this goes back to 1926, the market has been up about 18 percent, on average, in the next year," Leuthold says.