He simply played the game the way it had to be played in order to win. Had he not done the necessary, the likes of Ullrich, Pantani, Basso or Vino would have assumed the mantle. You'd probably have to go through at least the first 100 finishers in order to find a clean rider.
Actually the notion that it's a level playing field just because everyone dopes is false. Different people benefit to different degrees when using a particular performance-enhancing drug. If you have a hematocrit of 48% naturally, raising it to 50% with EPO is not going to make much of a difference compared to someone who started off with 42% (50% is the maximum allowable under the new biological passport rules).
Also some people have more money, better doctors, better drugs, better drug-masking techniques, better info on off-season drug tests. Guess which athlete has had it better in every way?
And then you penalize those who refuse to take drugs for whatever reason. Some of these 'natural' athletes could have been a potential 7-time TDF winner, but they quit the sport in disgust.
I don't know whether Lance was the best cyclist out there on natural ability. (Some of his cycling team mates from his amateur years said that he had always lagged behind on the hills in training, and everyone had had to wait for him in the team bus downhill.)
But he's certainly the best doper out there - doping to win, passing doping tests, bribing test labs, committing his teammates to the omerta code.