WASHINGTON/FRANKFURT (Reuters) – Central bankers who led the charge to pull the global economy from a cliff during the financial crisis now risk becoming bit players, ill-equipped to snap the world out of sluggish growth and its addiction to cheap credit. Despite near-zero rates and $7 trillion of monetary stimulus unleashed by central banks in major industrial economies, investment and growth is stuck below pre-crisis levels and tepid demand is hurting developing economies by depressing prices of their commodity exports.