obviously the established ones will have more credibility because they actually have proof to back up their claims compared to new ones where you just have to trust them blindly they might say they have the newest system in place but the question is does it work?
Your thought is questionable in my opinion, you realise that in quest for promoting reputation or increasing the trust of users new casino might take KYC protection for its users more seriously than established casinos, because established casino might not recognise some decrease in users or disatisfaction of users because they have alot of clients so they my not bother but small casinos value every single user hence might be more likely to have higher security stands in KYC protection to build the trust.
With that argument, we can't absolutely say that a casino, whether old or new, will stay true to their KYC regulations. Because like it or not, all of them are vulnerable to hacking and other online threats. So even if the casino doesn't want their data to leak or be compromised, you would never know when such situation may happen. Hence, as a user or player, just submit kyc to casinos that you regularly use, not just any other casino that you are getting tempted with their perks or bonuses.
Of course you're right, every casino is vulnerable whether old or new, experienced or inexperienced casino yet the fact remains that asong as we have agreed to submit our KYC we should at all senses of reasoning know that it's never going to be safe, hence come to the conclusion that whatever happens, we will take them as it is or maybe with a unique voice be compensated if such happens. perhaps those who are privacy oriented understands this and hence to do gamble with centralised casino where KYC will be submitted.