Not really a question of evidence.
Santos Dumond was living in Paris, in the middle of the most air-enthusiast crowd in the world. There is no information about anyone actully denying that he did it years before.
The remaining fact is, that the Wright brothers actually flown a catapulted winged device, that could only fly with favourable winds , which was actually not very different from what you would get with a hot air balloon.
Dumond flew an actual plane, that could take of on its own power.
The only problem with the Brazilian, is that he was not born in north america because if he had, nobody would have ever talk about any Wright brothers.
The funniest demonstration of the flaws of the Wright's model can be seen 100 years later with president Bush presiding the 100 years cerimony.
he was told to leave before the 100% exact replica was demonstrated, because there was a great chance the device would not get airborne.
In fact, the president was saved fron an embarassment.
100 years later, tha replica, did not fly.
The Wright brothers didn't have a plane, they had a much better equipment. They had Hollywood, and that is the greatest dream factory in the world.
And dreams make the world fly.