If you wager 500 million to win 1 billion, then that be pays 2 to 1. Any 2 to 1 wager makes sense when the odds of winning is greater than 1/3.
If the odds are 50/50 or 1/2, then betting the amount to win the same amount is an EV neutral move.
You are correct that the marginal utility of money is pretty weird when you are billionaire.