It depends, does he 'ride light'? If top shetland is experienced, he will magically only weigh 50kg once mounted. However if he's a novice, he'll magically double in weight. And of course, you'll get a more honest answer from someone who'll make financial gain from one pony riding the other. Tbh though, pony hasn't collapsed to floor, which proves all horses are up to carrying 100% of their own weight.