The bank's latest investor survey reported a record proportion of funds considered equities as overvalued even while overweight positions hit multi-year peaks.
"There is a lot more private wealth and saving that's flowing into markets. GDP growth over 6 percent in the world's second-largest economy (China) produces an enormous amount of wealth and that's only one country," said Mark Haefele, who oversees around $2 trillion in strategies at UBS Wealth Management.
Not Euphoric
But if demand is buoyant, supply of equity is not.
In fact net supply was close to zero this year and last year because of share buybacks and weak IPO activity, JPMorgan pointed out in a note. Funds meanwhile invested around $359 billion this year, after accounting for reinvestment of dividend income, it said.
"The increases in demand...have had a strong impact on the equity market because of close to zero net equity supply," JPM told clients.
Haefele was among summit participants betting on equity gains in 2018. Equity sentiment among clients was not yet "euphoric," he said.
Many dispute the rally is flows-driven, arguing the key draw is earnings growth at rates that are smashing expectations.
Luca Paolini, chief strategist at Pictet Asset Management, is in that camp. He says first that 16-17 percent annual equity returns are "absolutely average" in a bull market, and second, the gains are only slightly outpacing earnings growth which is running around 15 percent.
"The price-earnings expansion is just 3 percent. This is not a market driven by flows, otherwise PE would have gone up a lot more than 3 percent...this is a market driven by fundamentals," Paolini told Reuters in a phone interview.