User blog comment:Maki Kuronami/Weapons Guide (Basics)/@comment-151.227.186.29-20150530165204/@comment-25857155-20150531224648

A ridiculously large sword made from superlight material would be nearly as difficult to use, and would negate half of the bonus of using such a weapon. It would be liable to interference from wind resistance and the like, would be difficult to bring much weight to bear with each strike, and would be next to useless against a weapon of similar size and greater weight unless the wielder was strong enough to counter, in which case he/she may as well use the full-weight version anyway.

Wielding two swords of that size would be simply absurd - the blades would most likely strike each other more often than anything else, and the wielder's strikes would be weak, imprecise, and slow - ergo, useless.