It does make sense but it does not represent my experience with medieval weapons. With hand weapons, the size of the wielder does make a difference because they get better leverage on the weapon.
At 5'9", I actually have considerable difficulty using a claymore one-handed. But my 6'6" fiends does not. It simply comes down to the ratio between the height of the wielder and the length of the weapon.
With a claymore, two-handed, I strike between 380 and 450 lbs of force. My 6'6" friend will strike between 220 and 350 lbs one handed. I don't even get to 200. This is simply because of his height and mass. It's easier for him to move the weapon. He struck at over 500 lbs two handed. And he's not that much stronger than I am oddly enough and only 20 pounds heavier last we checked.
After 7 years of practicing martial arts with medieval weapons I've come to the conclusion that a larger person could potentially use a two handed weapon (for average size individual) one handed with the same amount of force because of the greater leverage that person has on the weapon.
The reverse goes for smaller individuals. Anyone under 5'2" would never be able to use a claymore one handed. The weapon is simply too large. And with their reduced leverage on the weapon, the amount of force they can put in the weapon is also effectively reduced.
The claymore we use is 47.25" in length from tip to pummel. It weighs about 2 pounds. The pummel reaches the bottom portion of my sternum. Technically, that is a two-handed weapon for me. And considering how unwieldy it is one handed re-enforces this with me.
This is the basis of my house rule:
A creature/character can use a weapon of equal size or small one handed and one size larger two handed. The size of the attack depends on the size of the weapon. Some weapon fit within two size categories, they can be used one handed as the lower size category and two handed at the higher size category.
As example of Medium-Large weapons:
Bastard Sword, Long Sword, Claymore, Katana and Spear.
Small creatures would use these weapons two handed as medium weapons. Although I wonder how a 32" tall Halfling would manage with a 47.25" long sword, but I don't want to go down to that level of detail. But an Ogre would pickup the same weapon and would make a large attack.
Better leverage goes a long way.
So I will leave Giantism at 25 DP but it will essentially be the same as Enlarge (Minor). In the case where a character with a race that has Shrink (i.e. Halfling and Gnome), it will cancel out Shrink and become Medium size creature.
As a little historical note: the claymore and the long sword are essentially the same weapon. The bastard sword (or hand and half sword) is the precursor to the long sword, a broad sword with a longer grip of sorts.