I've never considered using Ethereum on gambling websites. Even though the transactions are much faster compared to bitcoin, its high fees are not worth to use it on gambling. If a gambling website is a dapp platform where you just need to connect your wallet with funds, I would still not play there if they only support erc-20 network. There are many alternatives now that has low fees like polygon or bsc network to gamble.
Speed of transactions are depends on the fee you have paid, there's no difference between Bitcoin or Ethereum. If you send Bitcoin and set the fee with high priority, your transactions will confirmed around 5-10 minutes. As you said Ethereum is much faster than Bitcoin, you can send Ethereum and set the fee with low priority, I believe your transactions might confirmed around 1-2 days, even more it will stuck in lambo.
You can still use other network and connect with dapps, example BSC network.