I think money laundering if done is done through mixers more than is done in casinos although people may use casinos for small amounts which really is not considered money laundering.The casinos may serve a good purpose in making your coins anonymous as you can deposit to them through a wallet and receive money in a brand new wallet that you create and the tx id is different because the money is coming from a wallet of that casino,that is the maximum people can use casinos but criminals to launder money through them I find it hard to believe.
I think that the real money laundering is to ensure that the right person gets their hands on a completely legal fiat. "Winning" from the casino is still gray money, since you have to declare it and pay taxes (different conditions in different countries), so it seems to me that those who launder amounts of money at least a little more than small ones use other schemes.