Dwyer said that valuation expansion would continue to push stocks higher, although he expects a bit more of a correction in the near term.
"The direction of earnings is driven by economic activity. Economy activity is driven by the slope of the yield curve and availability of money. We've seen the loan demand data pick up pretty appreciably," he said. "The steepness of the yield curve is driven by Fed policy. Even with a rate increase earlier than expected next year, it's still historically cheap, and that's driven by core inflation."
Dwyer was confident about his thesis beyond the May-to-October period.
"All of those factors, even if you look out three or four years, remain positive, which means there's no way that a pension or endowment fund can get 7½ percent unless you're in a levered credit fund, unless you go into equities," he said. "And I think that ultimately is the driver."
Read MoreDon't laugh: There's logic behind 'sell in May'
OptionMonster co-founder Pete Najarian took issue with the sweeping sell-in-May advice, noting that certain sectors, such as financials, could still outperform.
"I just hate the blanket statements," he said. "It's like somebody saying, 'Everything in tech's getting sold.'"
Ritholtz Wealth Management CEO Josh Brown added that the data going back to 1928 suggest that in a mid-term election cycle May on average actually shows a negative 2 percent return.
"So, if that happens again, the question to ask yourself is: Is this really important for me to react to? And I think for most people, probably not," he said.
—By CNBC's Bruno J. Navarro. Follow him on Twitter @Bruno_J_Navarro.