Could you please tell me if there's anything wrong with this sentence? Any comment/s would be appreciated.

He should be soaring like a bird on winning the race, but he was falling like a stone instead.



Well, difficult to know without a context. Is a character saying this about himself or about someone else? What kind of race was it? People can make a race out of a lot of things. Was the race open to both sexes? All of those things can influence wording. Technically, it's not bad, except I'd change "on" to "upon". Stylistically, I think it's pretty awful. Those "ing" verbs sap the energy from the sentence, and "soaring like a bird" and "falling like a stone" are cliche, not to mention abstract and vague.

Suppose they're racing carrier pigeons, the winner has a reputation for arrogance in regard to his birds, and a friend notes his reaction to the win. A better way to describe this is through the winner's actions, not some vague commentary on his supposed mental attitude. Plus, you could throw in some "birdy" type words, like this:

Normally, his victory would produce an insufferable strut, but he walked by with an almost disappointed plod, and where he would usually crow about his win, he now remained silent and inscrutable as an owl.

See? Don't simply tell his attitude, show it through his actions.