Using a new casino that doesn't have any good reputation yet is not proper because most new casinos normally have systems issues, that's is why most times when a gambler wins he finds it hard to withdraw the money that he won, and delay on deposit is also another thing we wouldn't want to think of.
The old casinos are the ones we can fully trust because they have built their reputation and they wouldn't won't to risk losing what they have built so far. However, putting a trust in the OP won't end well.
You have a point only that you looped it together, the old casinos are better, especially if they have a good reputation with track records of minimal complaints, they will surely deliver excellence to the gambler. I also hope they are well capitalised because it's another issue regarding whether you are in the industry for long and have a few complaints, what if the ones with huge wagering and withdrawal requests are not paid? These are also what we should look at when considering the new casinos.
The issue you raised about their system is right but the more concerning issue is whether or not they will pay you, especially if you are withdrawing big. Some of them may have that amount to pay but due to greed they might seize it for themselves, so it's riskier to opt for a new casino that is just starting everything, who knows what they would become? Experience has taught us that.