Ironically, during the anti-trust trial of Standard Oil, Rockefeller's market share kept slipping. His competitors figured out how to compete with him.
As for Rockefeller being a "robber", the rise of Standard Oil resulted in the price of kerosene dropping 70%.
If technical advances make cost go down 90% but prices only goes down by 70%, someone is making tons of money at the expense of consumers.
That's what happened with the telco by the way, the price is is still significantly lower than 40 years ago, but in the US it's still more expensive than it should.