aviation is aerodynes old chap.
I don't know which sources you choose to support that statement, although I can guess.
According to the New Oxford Dictionary of English, Aviation is the flying or operation of aircraft. (i.e. a machine capable of flight)
This includes the two basic categories of aircraft:
(1)aerodynes : primarily aeroplanes and helicopters which use self-generated aerodynamic force to stay airborne ( and which does not include sailplanes) and:
(2) aerostats, including dirigible airships, which do not require using self-generated aerodynamic force to stay airborne.
I have noted in the U.S.A. already that the definition of "aerostat" has begun to be misunderstood by the scientifically illiterate, being increasingly confused with that of "tethered aerostat"
Perhaps you would like to give the many writers of aviation history reference books who have , mistakenly according to your reasoning , started with the history of the pioneers of ballooning and gliding and the developers of airships, the benefit of your superior knowledge?
But then of course, according to you, the Wright Brothers "invented the airplane".
P.S.
I'll save you the first stop on your search:
The modern age of aviation began with the first untethered human lighter-than-air flight on November 21, 1783 of a hot air balloon designed by the Montgolfier brothers.
Wikipedia under : " Aviation"
(Doubtless, like Simplex1 ,you will be able to find some other "definition". )