People will always find a way to justify winning or losing, but honestly it's entirely RNG. Seriously, just take your winning/losing horse and then flip it. You won because you had 450 wit, now tell yourself you LOST because you had 450 wit. "I lost because I only had 1000 stam" and then you'll have some mouthbreathing retard saying how he won because he'd managed to get enough stamina (900). Both sound "convincing".
So many factors affect a race's outcome that even a 600/600/600 uma could beat a 1200/1000/900 one by a landslide if she got a little lucky. In reality nobody knows SHIT about this game. Statistics is bullshit and I don't even feel good winning anything in this game.