Weight is a factor, but not as the current handicap system is.
The spread in weights is simply not enough to efficiently handicap a good horse, nor favour an outsider.
In fact so many winners have been ridden by jockeys up to 1.5kg over handicapped weight as expressed by Racing Australia.
Weight is one of those excuses that race callers and punters perpetuate, if the horse loses it's because of weight, if it wins "oh the topweight defied the weight".

The biggest factor is the way the horse is ridden, how much ground it covers compared with other horses and the ability to overcome being posted 3 or 4 wide and still win.

When it comes to Usain Bolt it is the equivalent of him carrying a chocolate bar or a box of matches.
Imagine though, if he were running without lanes that equal the distance for all runners, and had the outside lane instead so had to run 50m or 100m more.

That's my take on it.

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