I think your being a little closed minded about this movie. Its not that its a WWI or horse fantasy land its more for the impact that the horse made on peoples lives and the impossibly strong bond that certain individuals have with their horses. If you read the book it focuses on the different ways that joey is effected by people and vis versa.
The non horsey world is not interested in our day to day things we deal with, theyre never going to concentrate fully on the training, and everyday care of horses, theres only so much time for the movies plot and they can't waste it on training, ya joey and his and his bff sorted the pecking order out in like 2 min but they can't waste time showing horses strut around trying to choose the dominant one. Theres much more important scenes and situations to show.
Ther were some very realistic and accurate scenes too. Yes joey may have seen a tank before but he just lost his friend, been abandoned by the other horses and humans and had a giant metal monster come towards him, trapping him next to a fence. I think that's a VERY accurate depiction of how a horse would react.
As for the ending, theyre trying to capture the full audience, they wouldnt get as much reaction from a hobbling horse as from a horse that is overjoyed to finally reunite with his owner...i agree pretty dramatic but they want that happy ending.
The CO didnt ban him from buying him he said he couldnt GIVE joey to them. Its pretty accurate for the situation. They just finished a war, and the army, whether american or otherwise, is not just going to give a valuable asset away, they try to profit from what they have.
Theyre not trying to make everything into pupply love. There really ARE horses out there that would love, live and die for you. I HAVE had horses that risk their own life and limb for my or someone close to me with their horses. Ya it might not be an every horse thing but some people do have that bond.