That's correct, OP should convert his BTC to ETH if he wants to enjoy a minimal fee, that'st he only way as transaction fee for bitcoin today needs to be higher for fast confirmation. Sportsbet is not charging fee for withdrawal and that's the benefit for using the site.
Or....
Send your entire bankroll so you don't have to send every time, like I said withdrawal is free, so you'll enjoy it.
Yes, that is why I always do that because eth is always minimal fee so, try also witdraw using eth. because btc now high fee because of btc price.