I said the currency should be btc or mbtc, first please understand my comment.
Why it should be btc or mbtc? Just because we are in the crypto gambling industry so a site that accept crypto should not use fiat as the main currency to bet?
It is very common now, many sites use $ as the main currency although players are able to deposit with some different crypto.
Some sites do auto conversion (crypto to fiat) and some others keep the crypto but the they have an option to show balance in fiat.
I also find it very convenient when the casino combines fiat and cryptocurrencies. In this case, the advantage of fiats proves that it is more a classic casino than a cryptocurrency one.
However, I think it's easier to add cryptocurrency payment than fiat, so probably soon the choice of crypto for us should be bigger.