Money manager capitalism is financial capitalism. But financial capitalism is only tangential to actual capital. It means money making money from money.
Put baldly it is rentier capitalism. Not concerned with machinery, or tools, roads or bridges, automation or labor but with numbers of digits on financial ledgers.
The money managers, whether managing their own, or other people's money, are primarily concerned with conserving and growing those ledger numbers abstracted from reality. Those become derivative instruments & they lose touch with the real economy, the inputs, real capital & other public goods, that drives a healthy society.
The numbers in such an economy thus become abstracted & unearned properties, & actually can threaten the people & things in the real economy.