We are not totally safe at all even if we choose those reputable casino since even government data is hackable so this data leaking could possible happen to those reputable casino since we don't know on how long they remain reputable since there would be fall down in their business especially if they can't adopt to the changes of their target market especially on new technology introduce on casinos.
If we know for ourselves that we are vulnerable since we are well known individual or known to have a lot of asset then I guess gambling maybe is not for us since we will be the target of possible attacks since our data's would be sellable to those criminals used other information just to take advantage on certain situation. What only thing we can do here is we need to be prepared on situation and think about next action if data leaking will happen to the site we are participating in.
If you ask me, I did tell you that only the dead is safe or save as long life and live in this world is concerned.
I've heard a story of a man who slept and dreamt that he died and was being buried in the dream, that morning, he woke up and said that he will be staying at home all through that day, because probably, death have set trap for him on the road, which is why he had that dream. And later on, just some few hours into the day, he was just coming outside from inside his house, a cow skull he hung on the ceiling lose and the sharp end pierced into his head, he was rushed to the village hospital but he later did not make it, he died that same day.
The above is actually a true live story, and what that teaches us is that, what ever have been destined to happen will surely happen, no matter what we do or avold, if its been destined that your personal information or document will appear in the hands of criminals, that we surely happen no matter how far you run away from casinos where kyc is must

, but on the other hand, if it's destined that such will never happen to you, then kyc even with an untrusted casino, your personal data and information will surely remain safe.
So, personally, I feel that what we owe ourselves is to make sure to avoid casinos we know that is generally distrusted, we should only kyc on reputable and well trusted casinos, every other thing is in the hands of our creator(God).