As a regular gambler before. Altcoin is indeed the best alternative because you will just need to send your Bitcoin on Exchange to convert it on Altcoin then problem solved for expensive fees.
Altcoins are convenient for gamblers because they usually don't use big money for gambling. They have to save their transaction fee for gambling and they will choose altcoins, except Ethereum, to save transaction fee then use that saving for gambling more.
Transaction speed is another factor that is like by gamblers too. Altcoins can help them to save time of waiting for transaction confirmations and get credit from casino to start gambling.
But LN is really good implementation to a casino so that Bitcoin holder can still hold and gamble at the same time. It’s just not that popular and a waste of resources for casino side.
The problem with Lightning Network is you must use on chain first before can use off chain Lightning. You need to do an on chain transaction to open your Lightning Network channel and it requires costly on chain transaction fee.