I was wondering any reason in particular why BlueWallet would be better than Blockchain.com in regards to betting sites?
I don’t think he meant anything explicit in the context of sports betting or gambling, but that it’s much better to have complete control of your private keys in a non-custodial wallet - than to have confidence in online crypto wallets. It is true that blockchain.com allows backup (seed words), but there is always a danger that someone will hack your online wallet - most often if you click on the phishing link and in that way expose your login information.
However, it should be noted that some online wallets or crypto exchanges have a ban on transactions with gambling/betting sites - so it is always better to use a desktop/mobile custodial wallet.