For serious competitive play, all players should have the same opening split, or get to choose 5/2 or 4/3. Chapel games tend to make this weakness obvious
I would consider the Dominion League[1] to be serious competitive play, but it doesn't require that (also the current online client doesn't support that, presumably due to lack of demand) but what it does is to balance which player starts first, which can often lead to wins since in the end the game is often decided by a single turn.