You're not wrong but nobody knew this in 190x nor could it have been reliably predicted because most of our knowledge about how low pressure gasses flow over surfaces in unconstrained environments (i.e. the atmosphere) comes from aviation which didn't yet exist in 190x.
The state of aerodynamics in 190x was more advanced than I suspect you imagine, with Lanchester on the right track in thinking about vorticity. Here's an interesting article on the divide between theorists and practitioners (which the Wrights partially, but not completely, bridged - and the theorists were evidently not all communicating with each other, either), and it also mentions the flawed assumption, of flying being like boating, that I mentioned in my earlier post.
https://www.aerosociety.com/media/4846/fw-lanchester-and-the...
It also shows that Lanchester, regardless of his theoretical chops, was not a successful airplane designer! He comes across as putting too much emphasis on how he thought things should be.
The Wrights clearly didn't. Around 1979 a Caltech scientist did a study on it, and determined that the flights of the 1903 Flyer went about as far as they could have due to the instability. At the 100th anniversary, a couple of exacting flying replicas were built, and flew about the same distance.
I'm not sure about this, but the mathematics of stability and control theory had not been invented at the time. These theories were developed alongside electronics.
However, it was still known that one puts the feathers on the back of the arrow, not the front. Just try shooting an arrow with the feathers on the front. It promptly turns around so the feathers are at the back.
I recall reading somewhere that most of the Wright's competitors (maybe not Lillenthal) imagined flying to be like boating, but the Wrights realized that it would require more-or-less continuous input from the pilot to stay in control. I wonder if their profession as manufacturers of bicycles predisposed them to this insight.
[1] https://www.flyingmag.com/photo-gallery/photos/awesome-airpl...