Slow transaction fee on the native Bitcoin blockchain is still quite high compared to the current fees with fast confirmation. Betfury charges 0.000075 BTC as you said while my recent transaction only caused me 0.00000747 BTC (3 sats) and that was confirmed in 10 minutes. Anyway, adding BSC as an option is great but it would be a lot better if they can also check/adjust fees every 2 weeks. I hope that's not asking a lot.
Have you used the segwit address for your transaction? If so, such a low fee (747 sats) per transaction is typical as long as the mempool isn't overloaded. Anyway, I agree that the 7,5k sats fee for slow withdrawal is still high. It would be great if they add the bech32 address for withdrawal as an option. However, I think betfury and other gambling sites won't bother about it.