Steadman most certainly did not use drugs to produce his best work..
I am not sure drugs inspired the best work of anyone on that list.
Huxley wrote Point Counter Point and Brave New World years before LSD was synthesized. I believe a dinner plate was partially responsible for the work that won Feynman a noble prize. Steve Jobs main ideas came from a visit to Xerox Parc. As much as like Carl Sagan I am not sure he added anything groundbreaking to science, he was just very good at explaining what other people had discovered.
Erdos was a legitimate genius imo..