alt Hacker NewsThe way to determine how you know if you have picked the best horse to clone would be the secretary problem[1] for optimal stopping. This is somewhat plausible among polo horses because of the artificially small population size of pedigreed and trained horses.
The simple version of the problem is you ride about 1/e of the total population and then the first one that is better than all previous ones is your best option. For a pro polo player who would also breed and train others in the off season, over a multi-decade career, it's not perfect, but in aggregate, they are positioned to be pretty good.
Will there be black swan horses? Absolutely. They aren't even black swans, they're inevitable, but if your goal in the sport is to compound your average performance over time without significant setbacks (loss of a prize horse), then cloning a top player's best horse is a good bet.
I find the ethical discussions around horse cloning and sports lack a lot of domain competence in both what riding is, and the stewardship and biology it entails. From a sensory and ontological perspective, a horse is basically an alien being with a peanut sized brain that it falls to our species to be responsible for its existence. Cloning a few to adapt them for survival in our world is profoundly more humane than selling the surplus from breeding programs for meat or leaving them for predators and disease. Even though the philosophers comments about objectification were paraphrased for publication, their perspective is dumb.