The comparisons between athletes of different era's is really pointless and at the same time human nature. We can't compare the Gale Sayers of his era to Barry Sanders of his because ALL the players of Barry's era were bigger faster and stronger. This is true of any sport. Ali would be a light heavy weight today. If Merkx and Moser were riding today they would be different riders. They would be making pile more money and they would not have to race crits days after the tour just to make enough money to feed their families. For better or worse times have changed even since LeMonds days.
Many riders take substances that are only legal because the WADA has not discovered them yet. For many years riders took all sorts of drugs from anphetimeans (sp) to moraphine and they were legal. It's all changed in every sport.