It is helpful to prevent money laundering with small amounts, you're missing a point, but I agree that people who launder money with big value, this wagering requirement won't help to prevent it. There are other ways to do money laundering and people who want to do this, don't need to take risk by doing it on a gambling site and face with risk of losing money by wagering.

Wagering requirement is like KYC, can be helpful or not helpful against money laundering, it depends on different users but both exchanges and gambling sites get benefit from KYC policy and wagering requirement, it's undeniable.