This cannot be true always, in final even a score of 140 can be match winning. Both these matches target was chased because of some brilliant batting first by neesham and michel and then stoinis and matthew way. These things cannot happen always. Because in batting first team think that they need to score 180 runs they may end up in 120 only, so they must only plan according to match situation
Well anything can happen in final but based on stats of this WC only in England, Sri Lanka game the side batting first won the game rest victories are on associate teams. Under lights it's very difficult to defend. Side batting first need to heavy runs as score of 140 , 150 is nothing Under dew.