There are many disputers. One thing they all have in common is a complete lack of evidence. Ader, for example, pops up 17 years later saying he flew. But he's got no airplane, no witnesses, no photo, no followup - just a drawing. Even worse, he claimed an altitude of 3 inches - about what you'd get from going over a bump or a gust of wind.
And does anyone really believe someone would toil away for months/years, build an airplane, make one flight with it, not tell anyone, dismantle and trash the airplane, and forget about it?
Nope. I'd be flying all the time showing off my creation.
1. years of notebooks where they logged their ideas, progress, data, designs, etc. The notebooks clearly betray their understanding of what they're doing
2. a clear photograph of their first flight (a contender for the greatest photograph in history)
3. witnesses
4. a stream of prototypes leading up to the first flight
5. a stream of improved machines after the first flight
6. many demonstration flights
7. the original machine was preserved and sits in the Smithsonian for anyone to examine
8. exacting replicas have been built, which fly and exhibit flight characteristics that match what the Wrights described
The other claimants have literally zero of any of these.
However, it is certain that they carried out the first non-negligible, directed, flight.