Nonetheless there are still large, fairly high-damage weapons with high accuracy (greatsword? landsknecht?)
But please don't reduce cleave into a skill where you can either use a small accurate weapon and deal no damage or a huge weapon and never hit
As for scythes, they certainly look like cleaving weapons. But the truth is you simply can't swing one headlong into a person full force, like a sword or an axe or any normal bladed weapon. That is the idea behind cleave I guess. If you just look at the shape of it, a scythe really requires a more complex (if not awkward) motion to actually hit somebody with the cutting edge. The amount of force there probably isnt enough to do the kind of devastating limb-severing of the cleave skill (except maybe for the head)
As for war scythes, if there are any in the game then they should be another subtype completely.
Then again it's a fantasy world sooo...