Still, besides all this, I would also assume that the staff of the casino could easily ask for proof of origins of that money, in the case they noticed something strange going on with a particular user. Like some new account depositing much and, playing with high odds and has not completely gone through KYC, for example.
Not instantly casino will ask proof of funds. I think a standard KYC that requires Identity verification is enough for whale players that will deposit huge since casino doesn’t want scared them off. Proof of source of income is only imminent if casino is already have a lead to users account that involves on money laundering.
Money launderer is not dumb enough to bet using same pattern because it can be caught easily by casino security team. Launderer usually play like a normal player since they have a huge bankroll, They can’t be beaten easily by betting on 50% win chance rate bet using small bets. Launderers bet randomly to avoid making a bet pattern. OP suggestion is definitely not a loophole and a dumb ways to launder money.