So, it seems to me that weapons training can only inform your empty-hand training by starting with martially effective/valid weapons techniques,
The thing about this is, koryu training tends to involve years of practicing techniques before you learn how or why they are martially effective or valid. Or there is a story about their martial validity at the outset, and then later on you are shown that you have actually been practicing something completely different.
I agree that within the context of any system of aikiken, you need to be able to pressure-test the kata and figure out how they would work in a more fighty situation. Shinai are really fun for this.