Just to voice my opinion here, I do not support this new rule either.
In many games even an average player will have 4-5 heroes above level 5, from prisons alone. Players who like to develop side heroes will have 7-10+ heroes above level 5, once you dismiss half of them how would you keep track of who died in combat? Furthermore,I don't see how this rule is a solution to anything. Let's say both mains die in FB, then no one can rebuy either of these mains, so the game becomes an endless chain of scout fights on a map with 20+ towns. It's boring and there would be no motivation to play along.