Coppi wasn't a doper, and to be honest amphetamine isn't much of a PED. In fact I think it was largely banned because of the health risks rather than the fairly limited performance boost it gave.
Because it doesn't actually increase your physical capacity in any way, it just enables your mind to push your body beyond the limits that would normally get alarm bells ringing. This is what those riders were on, that and any random cocktail their soigneurs would swear make them ride faster and recover better. Drugs like amphetamine,cocaine and even caffeine have hallucinogenic, euphoric qualities that trick the mind, which meant you could push past the pain barrier, which in turn meant at the end of a race they'd need morphine injections directly into their legs to stop them hurting and let them sleep.
That coupled with a very basic understanding of human physiology and things like hydration made for a lethal combination, particularly on hot days, as Tom Simpson found out to his cost as a he wobbled to a stop on the slopes on Mt Ventoux. But the drugs didn't make their muscles bigger, their circulation better or their lungs more efficient.
EPO, steroids, AICAR, gene-doping, these are game changers and operate in a totally different way to those early PEDs.