Maybe that's the secret - just make all the weapons absurdly huge (they... basically are, really)
The end result will of course be that they are also crazy valuable and heavy, but that doesn't seem too unrealistic.
Let me see if I can get a more side-by-side image, but they are about as long as their wielders, generally, although not as thick all around as a person. I could see them being like half person-size, though. I myself found Size 900 to be an oddly small amount and had upped it since then (I've been updating the mod, originally made by Iados, with his permission), but maybe they just need to be absolutely enormous.
Here's one being swung away from the body, which at least gives a different perspective. Most of the other weapons are of similar size in some regard - Greatswords and Switch Axes are probably the next biggest, then Long Swords (about as long as Great Swords, but thinner), then Lances and Gunlances (some of these may actually be bigger than longswords, especially the Gunlances), with Swords being the smallest (about the size of a regular arming sword or short sword) among the melee weapons - swords designed to be used with shields are usually slightly bigger than the swords used in dual pairs, but since you can't force a weapon to be used with a shield I just sort of lumped them into one category.