First it wasn’t just him. The entire sport has been plagued by accusations that the top performers are doping.

Secondly, he won 7 consecutive races. When he dropped out, the race times didn’t change that much and now the Tour de France winning times are faster than Armstrong.

You can claim that it’s better bikes, training, diet etc. The simplest explanation given all the facts though seems like doping.

Of course it's not proof of cheating, but it is strong evidence not to trust the testing unless something very fundamental has changed.

And your argument strongly depends on accurate testing.

Proof, no, but the best predictor of future behavior we have is past behavior.