I doubt if there could be someone who is born with gambling talent, there is nothing like such, from what I've seen so far, I haven't met a consistent winner, everyone is always struggling with winning no matter how hard they try.
Even if there are lucky days, it does not even last longer, lucky days are always one day, I haven't encountered consecutive two days of winning, always one day of luck.
Imagine this, to be expecting a born winner, nah.
You are right, such kind of incidents are not usually a secret, if someone was born with such gift that they can win as they want, they will be making casinos go bankrupt. You understand? Even if it's just few persons that has such gift, they could use a very huge amount like $100m (or more, depending on the casino's maximum wagering amount) to stake in a game, knowing that they are going to win and by the time they win like that few times, the casino will definitely go bankrupt and they can move on to another casino. Such event will not be hidden but there's nothing like that.
If there were such individuals, the betting industry would not have been discovered. There are many lucky people in the world who have won a lot from casinos. It can be assumed that they are lucky by looking at their winnings, but is there anyone who wins every bet regularly? Of course not, which is not possible. You are right that if this were the case, the casinos would have gone bankrupt. Again, the person who could have known in advance would definitely not have been an ordinary person and would not have been greedy for money. In other words, it can be said that this is only possible in fairy tales, it has no basis in reality. Some people may be talented by birth, but in the case of betting, it is not possible to win in betting with that kind of talent. He may win in betting, but the winning will not be consistent.