I fully agree. If the errors, according to different points of view, have already manifested themselves. It makes no sense to continue arguing about the same thing.
It is not about arguing it is about presenting correct information to enlighten to those who still have doubts.
You said you consulted do not show representations of small horses in any case. All the information I provide are contemporary photographs, which in no case prove anything. Of course my photographs are contemporary. Camera was not invented back then and the first photograph made in a camera was taken in 1826.
Once again I present to you the precise and true information on Samurai horses the Kiso horse.
The Kiso has historically been used for agricultural as well as military purposes. In fact it is said that, during the 12th Century, over 10,000 soldiers used the Kiso as their war mount. During the Edo era, spanning the period 1600 to 1867, the Kiso was once again used for war and was bred actively for this purpose. The population of the Kiso horse rose to more than 10,000 at that time.
The Kiso horse is medium sized, standing about 13 hands (135 cm). Throughout the Meiji Era, Kiso horses were crossbred with many western breeds and the pure stain virtually disappeared. The breed is being preserved in the region centering on Kaida mura in Kiso County, Nagano Prefecture. There are today only 117 Kiso horses left, which are often seen in processions in local festivals. They are also used as riding horses.
Here are some links or you can google search it:
https://www.petmd.com/horse/breeds/c_hr_kiso
https://samurai-world.com/kisouma-samurai-horses/
http://afs.okstate.edu/breeds/horses/kiso/index.html/
It is regretful that most people’s lack of knowledge on the subject regarding Samurai. Sculptor Emmanuel Valerio who sculpted the Fort Duquesne Red Devil Commander once told me he saw in a figure show that someone had replaced his Red Devil horse with a bigger one because the person was being ignorant and unaware of the Kiso horse and thought the original horse was wrongly sculpted. That is a pity.
People who see all the big horses depict in the Samurai movies; woodblock prints and scrolls give the false impression that Samurai used big horses in their cavalry. As in the movie RAN directed by Akira Kurosawa, the horses were imported from the United States for the shoot.
Since you said all your pictorial manifestations of medieval Japan(engravings, scrolls, plates, drawings, etc.) consulted do not show representations of small horses in any case.
Here are some paintings and an e-book where Kiso horses are faithfully shown.
e-book on Japan horse riding history: The Paintings by Ebine Shundo on the Ceiling of the Yasaki Inari Shrine,Tokyo,Japan
HERE