While not generally in the habit of "defending" Armstrong, I have to disagree. The Tour duPont wasn't exactly a weak field, and it was a big race considering (below euro races but probably bigger the the ToC), and at a young age he showed himself there. He certainly demonstrated that he could climb pretty well. Secondly, it's pretty hard to determine where how he would have done w/o EPO, since by the time he started racing grand tours and racing in Europe, the playing field was already in disarray. I agree with Krebs, I think he coulda been a ton 10 GC guy, and a potential winner if the planets aligned, the right guys broke their collarbone and that year's course suited him. I certainly don't see him being the dominant guy though, by a long shot. Regardless though, it's all speculation. What we do know is that we'll never know...
Where I disagree w/Krebs is on the whole "bottle fetcher to Tour Champion" thing. This has already been answered: Bjarne Riis. He went from bottle fetcher to multiple time podium guy, numerous top-10 finished an a tour title. A true "donkey to racehorse".
There are two things to remember about the whole EPO thing and donkeys becoming racehorses. First, whatever the % improvement in sustainable wattage in trained athletes (which is what really matters, time to exhaustion is a red herring), whether it's 5% or 11% etc, there's always scatter. That's why it's an average some improve a good bit more than others. Secondly, a professional water carrier is still pretty fast! Take the worst professional rider and increase his threshold wattage by 15%, and you have a champion.