I think both the new and old casinos try as much as they can to protect their customers' data, but then again, we should all be aware that immediately we submit our document online for KYC verification, it's now out there, and we should be prepared for the worst. Any casino can be hacked, both old and new ones, and the older ones are even more of a target for hackers than the new casinos.
gamblers tend to trust the older casinos that have earned their reputation with all the challenges they must have face and didn't flinch, a pathway new casinos haven't crossed yet. Nevertheless, there exists no difference among them all in attempt to protect the data of customers but one thing which you have said which is certain is that they can be hacked. Although hack is one of my worries I also give concern about how these casino could face pressure from the authorities to make them share our data to them without the customers having a clue on this happening.