There was a hot debate about this awhile back, w/one poster insisting that at the turn of the century, the Wright brothers alone fully understood, let alone close to mastering the 3 symmetry axes (yaw, pitch, and roll) of a plane.
That was me and the point of my argument was mostly lost in the usual herping and derping about how the Wright Brothers sucked and how Sim Sala Bim of Etceterastan was really the first to fly in Eighteen Hundred and Umptyfratz.
The facts are this. Among the hundreds worldwide attempting to develop heavier than air flight around the turn of the last century, the Wrights were some of the very few who experimented with gliders, the Wrights were the only ones who built models and wind tunnels, the Wrights were ones who realized Smeaton's Coefficient was incorrect and recalculated it, and the Wrights were the first to realize three-axis or dynamic control was necessary for flight. (As a matter of fact, the Wright's patent is for the dynamic control of aircraft.)
Between the Wrights' breakthroughs around 1900 thanks to wind tunnel work, the confirmation of that breakthrough in 1902 with the tethered Glider, the 1903 Kitty Hawk powered flights, the many long distance 1905 flights in Ohio, and the Wrights' public flights in France in 1907,
no one replicated the Wrights' insight regrading dynamic control. In the first decade of the 20th Century, there were plenty of people slapping more and more powerful engines into various airframes, but none had realized the necessity for dynamic control until the Wrights' public flights.
The increasing number of flight attempts meant that sooner, not later, someone would have realized dynamic control was necessary and the breakthrough would have occurred. However, no one managed it during the period I mentioned.
Just how or when that breakthrough would occur will depend on the fate of the Wrights. Kill them off early, or otherwise stifle their interest in flight, and the breakthrough will come later. Kill them off after the 1902 Glider work and the breakthrough will come sooner because plans for the Glider were available. (One significant French aviation pioneer, Esnault, began to rework the Glider when new of the Wrights' 1903/05 successes were reported. He hadn't got too far when the 1907 public flights occurred.)
Ergo, w/o the Wright brothers, successful powered airplane flight could be delayed for another decade or so, when someone else to make the key breakthroughs in understanding flight dynamics.
I believe that 10 years is the outer limit here. By roughly 1907, too many people were making and failing at attempts at powered flight for one of them not to say
"Damn, I gotta figure out a better way to control this thing..."