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Unless your genetic make-up provides a specific handicap to effective training, the difference between people is not enough to provide a measurable advantage which more training wouldn't level out.
I am tiny, I weigh ~60kg, my bike weighs sub 7kg and can get about as low as possible. Jammy is 6'8", his ideal race weight is about 85kg and his bike, as you can imagine, is much significantly heavier.
Who is faster? Jammy. He trains CONSTANTLY.
p.s. I thought I read somewhere that Armstrong had a resting heart rate of about 4bpm and only built up about 60% of the lactic of most people. Obviously a bad example though, apologies.
The most important thing you can do to increase your chances of sporting success is to choose your parents well. Hard work and training is of course essential to success, but will only get you so far if you've got a crap set of genes