It was only after planes and parachutes (and I don't know how many parachute jumps had been made before Einstein thought about this) that people could have really experienced weightlessness.
Your sense of history is a little off if you don't know that balloons and airships were before airplanes.
As it happens, someone who was sort of a relative of mine made their first solo flight at the age of nine, which might still be the world record, and that was years before the Wright brothers.
On 19 September, 1789, a duck, a sheep and a rooster made the first balloon flight by living animals. The first manned balloon flight flight was on 21 November 1789.
Louis-Sébastien Lenormand (May 25, 1757 – April 4, 18371) was a French chemist, physicist, inventor, monk, and a pioneer in parachuting.
He is considered as the first man to make a witnessed descent with a parachute and is also credited with coining the term parachute, from the Latin prefix para meaning "against", an imperative form of parare = to avoid, avert, defend, resist, guard, shield or shroud, from paro = to parry, and the French word chute for "fall", hence the word "parachute" literally means an aeronautic device "against a fall". After making a jump from a tree with the help of a pair of modified umbrellas, Lenormand refined his contraption and on December 26, 17831 jumped from the tower of the Montpellier observatory in front of a crowd that included Joseph Montgolfier, using a 14-foot parachute with a rigid wooden frame.
André-Jacques Garnerin (31 January 1769 – 18 August 1823) was a French balloonist and the inventor of the frameless parachute. He was appointed Official Aeronaut of France.
Garnerin began experiments with early parachutes based on umbrella-shaped devices and carried out the first frameless parachute descent (in the gondola) with a silk parachute on 22 October 1797 at Parc Monceau, Paris (1st Brumaire, Year VI of the Republican calendar).2 Garnerin's first parachute was made of white canvas with a diameter of approximately 23 feet (7 m).3 The umbrella was closed before he ascended, with a pole running down its center and a rope running through a tube in the pole, which connected it to the balloon.2 Garnerin rode in a basket attached to the bottom of the parachute; at a height of approximately 3,000 feet (1,000 m) he severed the rope that connected his parachute to the balloon.2 The balloon continued skyward while Garnerin, with his basket and parachute, fell.2 The basket swung violently during descent,[Note 1] then bumped and scraped when it landed, but Garnerin emerged uninjured.2
His student Jeanne Geneviève Labrosse, who later became his wife, was both a balloonist and the first female parachutist. Labrosse first flew on 10 November 1798, one of the earliest women to fly in a balloon, and on 12 October 1799, Labrosse was the first woman to parachute, from an altitude of 900 meters.
So people were making parcute jumps for more than a century before Einstein. And some of htem might have experienced weightlessness for some time before opening their paracutes.
A number of people have survived falling from heights of tens or hundreds of feet. Thus the sport of making high jumps or dives into water began.
Cliff diving has been documented as far back as 1770 when Kahekili II, king of Maui, engaged in a practice called "lele kawa", which in English means jumping feet first into water from great heights without making a splash. The king's warriors were forced to participate to prove that they were courageous and loyal to the king. The practice later developed into a competition under king Kamehameha I, and divers were judged on their style and amount of splash upon entering the water.
On May 19, 1885 Robert Odlum was the first person to jump off the Brooklyn Bridge, and was fatally injured. Steve Brody claimed to have survived jumping off the Brooklyn Bridge onJuly 23, 1886, and the first confirmed survivor of a jump off the Brooklyn Bridge was Larry Donvan.
Lawrence "Larry"4 M. Donovan, born Lawrence Degnan5 or possibly Duignan2 (18623 – August 7, 18885) was a newspaper typesetter who became famous for leaping from bridges, first around the northeastern United States, and later in England. Inspired by the first successful Brooklyn Bridge jump by Steve Brodie, Donovan sought fame and fortune by leaping off that bridge, the Niagara Falls Suspension Bridge, and Bristol's 250 foot Clifton Suspension Bridge. Slightly injured on a couple of occasions and frequently incarcerated following his attempts, he struggled to capitalise on his fame, making money only through bets and brief periods working as an emcee or exhibiting himself in novelty shows. In August 1888, disillusioned and desperately poor, he accepted a spontaneous two-pound wager to jump from London's Hungerford Bridge late at night, but drowned in the attempt.
So some 19th century persons could talk about what it felt to be in free fall for several seconds.
I note that Jules Verne in From the Earth to the Moon was not the only 19th century writer of stories of space flight, and maybe some of them depicted weightlessness more accurately.
The First Men in the Moon is a scientific romance by the English author H. G. Wells, originally serialised in The Strand Magazine from December 1900 to August 1901 and published in hardcover in 1901,4 who called it one of his "fantastic stories".5
On the way to the Moon, they experience weightlessness, which Bedford finds "exceedingly restful".
"The Brick Moon" is a novella by American writer Edward Everett Hale, published serially in The Atlantic Monthly starting in 1869. It is a work of speculative fiction containing the first known depiction of the launch of an artificial satellite.
"The Brick Moon" was first released serially in three parts in The Atlantic Monthly in 1869.2 A fourth part, entitled "Life on the Brick Moon", was also published in The Atlantic Monthly in 1870.5 It was collected as the title work in Hale's anthology The Brick Moon and Other Stories in 1899.3
And I believe that Hale described weightlessness on the Brick Moon in orbit.
Somnium (Latin for "The Dream") — full title: Somnium, seu opus posthumum De astronomia lunari — is a novel written in Latin in 1608 by Johannes Kepler, and first published in 1634 by Kepler's son, Ludwig Kepler.
Kepler describes acceleration and deceleration on the journey to the moon and might also describe weightlessness.
Someone would have to read these, and many other space travel stories written before Relativity to see which ones might say that weightlessness in space travel is similar to the weightlessness feld when falling freely in a gravitational field.