This is too intrusive.
SoW is one of the standard practice of casino for AML, it's not just stake that ask for this, many other casinos also require the same for their advanced KYC verification. The whole process of this verification and why they keep rejecting things though, is not standard.
Although source of funds is included in the ToS of most of the crypto sportsbooks, there are sportsbooks that do not ask for source of funds. The rules seem to be the same everywhere, but invoking this rule differs greatly from sportsbook to sportsbook. The AML seems to be nothing more than an excuse looking for a way to take funds. All books seem to have a rollover. If someone is money laundering, it's obvious. They will 1x roll, or a small rollover, for a very large amount. Books in the UK and US ask for selfies but some of these books in CR ask for a video selfie. Your chances of being asked for proof of funds is higher at a book with a license in Curacao compared to the UK or US. It's suspicious when a Curacao book is intrusive for an obvious case where money laundering isn't involved. By taking a look at his deposit amounts and dates, there's no money laundering going on.