The rascally gadabout portrayed in "Amadeus" is complete and utter fiction. The movie is less a biography about Mozart than it is an object lesson in the conflict between excellence and average. Milos Forman and Peter Shaffer did the music world a disservice when they chose to play that lesson out against a backdrop of classical music.
One would think if there was a real rivalry, the two would have traded barbs in public. Kind of like Cruz and Trump do now. The alleged Salieri confession is not directly attested and was reported around a time he had gone insane and so who knows if he was kidding or imagined it.
The movie set off a long running obsession with prodigy kids who graduate college in their teens or younger. We had that TV series about a kid doctor for example in the 80s or 90s - I can’t remember. Moms were buying headphones designed to be played over pregnant bellies and other nonsense like that. I think the fad died when the first batch of kids turned out to be just as smart (or dumb) as the the rest of the pack.