Doping in cycling is cheating. Not everyone does (or did) it--see Christophe Bassons [1] as the canonical example--and in any case the most sophisticated doping regimens were only available to a few of the best-financed riders and teams. Hardly a level playing field [2].
Both valid points. It's sad that someone like Bassons is at a disadvantage.
You're right doping doesn't level the playing field. However, for better or worse it's part of the playing field. Of course, nothing about pro sports is ever fair. Money matters even taking drugs out of the equation. It buys you better bikes, trainers, doctors, training facilities, etc.
As far as some people responding better to drugs, well sports are pretty heavily defined by our bodies. Responding well to drugs is analogous to responding well to training, it's an asset for an athlete to have in today's world.
[1] http://en.wikipedia.org/wiki/Christophe_Bassons [2] http://inrng.com/2012/10/level-playing-field-doping-myth/