The very best-known names in asset management and investment banking are taking opposite sides in the talk over the classic way of constructing a portfolio—60% stocks and 40% bonds—after a disastrous performance for the 60/40 model last yr.

BlackRock says the losses—the worst in nominal terms for a 60/40 portfolio for the reason that financial crisis of 2008-9 and the worst in real terms in a calendar yr for the reason that Great Depression—show that the structure is outdated. Goldman demurs, arguing that the odd big loss is inevitable in any strategy and that 60/40 stays a legitimate basic approach. Strategists and fund managers at other large money managers and banks have been piling in on each side.