A keyblade is a not a realistic weapon. You cannot cut with a keyblade unless it has a edge, yet (as we already know) very few actually DO have an edge.
However, Sora still cut's through various items with ANY type of keyblade. This is not due to the keyblades natural edge , but with it's magical one. You would wield a keyblade like a club/blade hybrid (Noticeable in Soras unique Bash 'n Slash fighting style).
Now let's review.
A. Certain Keyblades MAY have a natural edge and they MAY have sufficient sharpness/cutting power to do a good amount of damage. This is overshadowed however by the keyblades MAGICAL sharpness.
B. The keyblade doesn't require a lot of force to cut things. Sora is slicing through buildings which (even if the keyblade is magically sharp and unbreakable) would require at least 30-40 tons of force behind it for such a clean slice.
C. Kari's keyblade was a stupid idea , screwed with the canon and was (frankly) the ugliest damn one in the game.
Overall Peach wins. Especially if she has her talking umbrella 😎