Excellent questions! Indeed, in betting and gambling, the interface is almost half the battle. If the site is slow, the navigation is confusing, and the cashier is hidden somewhere deep in the menu, no one will spend much time there. This is especially critical when you're placing live bets and every second counts.
The most annoying thing is when the design is overloaded with unnecessary animations at the expense of speed. The most appropriate approach is when everything is at your fingertips: finding matches in a couple of clicks, a clear coupon, and quick access to deposits and withdrawals.