Red Dead Redemption horse mechanics > Mount and Blade Horse mechanics
I really don't like kicking the horse repeatedly; like they do in RDR and SoTC. Witcher 3 should discourage hitting a button repeatedly but still get that same feel of riding a horse. It shouldn't behave like a car; like M&B. It should feel like you're literally controlling an animal.
It would be cool if they actually do realistic riding positions.
I am not sure I understood your post correctly.
Yes RDR was king when it comes to the "animations" and "look" of the horses (even showing their muscles moving under the skin in amazing detail), however "mechanics" wise Mount and Blade was much more realistic in terms of the actual controls and how you controlled the horse.
Basically how it worked was W went up a gait, S went down a gait. You could simply tap either one once (and let go) to move up or down one gait. If you pressed and held either, it would move into the highest gait or quickly stop the horse.
RDR, like many games, was more "gamey" with it's focus on repeated button mashing (to gallop) and not having individual control over every gait of speed.
If they could take the animations/details of RDR and the control scheme from Mount and Blade that would be perfect imo.