If Lemond was doping the decline in his riding would not have been so quick, if you watch the tour in the 80's only select groups were left in the mountains and today you hvae 20 plus riders heading into the final climb. During the 80's only the top riders were left at the end of a stage, and these riders were always near the front in all the classics and tours.
Yes doping was and has been always present in cycling, but doping did not really take off and provide a real benefit until the mid 90's prior to that the use of doping products was more of a recovery aid and not an aid to enhance the overall performance of a rider.
And Lemond, Hampsten, Roche and Kelly never ever had anyone accusing them for doping and did not have special trainers, and they did not go off and have a special training camp in the mountains during the summer. I think the truly gifted riders do not need to dope and I think Armstrong, and Julich can be counted in this group.