Doping has developed more than anything else in the sport - more than training and more than shoes - because science, medicine and pharmaceuticals are constantly evolving, whereas the principles of training have changed little in decades and shoes are technologically rudimentary compared to drugs. But until the early seventies doping wasn't known to be a significant feature in distance running because the drugs before that era were not known to enhance stamina - as blood doping and, later, EPO were found to do. The drugs that were available were mainly in the nature of steroids, that aided strength, and stimulants, like amphetamines, and were used chiefly by athletes in speed, strength and field events.
But once the genie was let out of the bottle athletes would use whatever would give them an edge, and so doping became endemic in sport and big business. The result is that it is now impossible to separate doping from the sport, whereas in Elliott's era you would have been pressed to find it.
What this means is that in the more distant past it was likely the best in the sport weren't doped, whereas now the reverse probably applies. It is hard to imagine athletes today making championship finals if they aren't doped, let alone winning or medalling. The reason is simple; they are going to be better if they dope - sometimes much better - and when the differences in ability at the top are so small the gains from drugs will make all the difference in outcome.