Neither is really good. Now it is just mayhem and before it was limiting to where you should play and penalizing you for playing in higher leagues than your cards should allow.
But if the split is again on the table I guess this includes the option to split the reward pools per card level segment, so why not split modern (and wild respectively) into modern-bronze, modern-silver, etc.? That way you create a competitive environment for every spending level and keep them strictly separate? With energy being a thing players would be kind of forced to choose a league, at least if they are trying to climb the leaderboard. Is the worry lack of match-liquidity?