Remember everyone, cleave isnt about mowing through 'weak' opponents, it is only about getting some benefit out of a finishing blow. One could even cleave off of the bbeg into his minions in the right circumstance. It could also be said that it is 'unfair' that they were attacked after the person already used their attack on the guy next to them.
Still, it isnt about 'weak' opponents, it is about getting a benefit out of the finishing blow (a twohanded pickaxe crit from a rageing, powerattacking barbarian and a bursting xxx weapon could take down a full hp massive creature, but it would still allow for a cleave). Much like getting an extra attack in after a trip or your opponent being unarmed after a successful disarm.
Still, it isnt about 'weak' opponents, it is about getting a benefit out of the finishing blow (a twohanded pickaxe crit from a rageing, powerattacking barbarian and a bursting xxx weapon could take down a full hp massive creature, but it would still allow for a cleave). Much like getting an extra attack in after a trip or your opponent being unarmed after a successful disarm.