Looking at the butterfly, the only central midfielders you have are the two MCs, no AMCs, no DMCs, so the opponent's central MC, if he has one, will only be marked by those two players.
So, are you trying to tell me that the Butterfly formation weakness is the lack of midfield MCs? I thought 2 MCs is enough to fight against 2MC of 4-2-2-2 Hexagon. Why this butterfly formation cannot beat the Hexagon?