However, some potential fraudulent sites also tend to become reliable if lots of rewards and winnings tremendously influenced huge subscribers. That's why being vigilant is encouraged as well.
When was the last time you have heard top casinos lose gamblers personal data or were hacked? Since they operate with money, and huge amount of money, they must have had a top level security. I really have huge doubts that if someone tries and managed to hack a casino, he will be there for users private information. Nowadays, people have already left so many pieces if private information everywhere, that being frightened that their private info will leak from casino is silly.
It doesn't work like that. You think that since a company is one of the leaders of the industry it has to protect the data well? Just look how many well known companies had breaches and hacks. How many of them used flawed software?
I'll post just one recent example:
Toyota has admitted its systems were breached. The Japanese automaker confirmed that approximately 240GB of data posted on a hacking forum by the threat actor ZeroSevenGroup originated from its systems. Toyota did not specify how many customers were affected by the breach.
https://cybersecurityventures.com/intrusion-daily-cyber-threat-alert/
Be aware that your KYC data can be leaked and it doesn't matter what casino you choose to play at.