The charge back abuse is new to me. This is really prone to abuse if casino allows card provider to charge back their customer loss.
I agree with your statement.
Generally, bonus abuse and collusion happens frequently in this kind of space but the limitation would be to have some sort of minimum withdrawal deposit for it to be claimable. This is also the reason on why some online gambling companies are hesitant to implement some sort of bonuses since it is subject to abuse by whales in the long run.
I remember back in the days, a person can basically abuse giveaways by creating multiple accounts and using referral codes of streamers. I guess this kind of abuse does not happen anymore or at least less nowadays.