Note that in 1913 U.S. economy as a whole was probably 20 times smaller, even after adjusting for inflation. So, JP Morgan had a relatively big chunk of money as a percentage of real gdp
Moreover, capital was far scarcer then than now. If you needed to raise money for an enterprise, there were fewer places to look for it. Consequently, Ol' Pierpont had a great deal more politial power than someone with the same amount of cash might today.