When has any country in the history of the world ever been unified "peacefully" based solely on economic policy?
The European union and United States are very much such economical and political unions. It is just unprofitable for members to wage wars with each other nowadays. This is also the reason why the economies are so strong.
But that isn't really important at because it's impossible to cleanly sperate "economics, agriculture, medicine" from "the military"
She could have divulged minimal information, localising the effects to a minimum. While agriculture, economics, and medicine affects the military - it can also affect the reasons for waging wars. You can just make it unprofitable to wage wars due to economic relations and interdependence - not unlike what you see between first world countries today.
do you really think Oda Nobunaga couldn't come up with the ground-breaking idea of "feeding my troops with all this surplus grain" on his own?
No I do not think so - in fact I criticised the stupid idea that only she could come up with this when it came up. The point is that she created this surplus for Nobunaga (he was amazed that she produced so much - she could easily have it toned down), and didn't try to spread her knowledge around instead. Additionally, there's still a large difference between giving out military ideas and agricultural ones. In one case the military effect is a byproduct and a lot lesser.
Do you think a country in the 1500s that has its farms outputting food at 3 or 4 times efficiency
Already addressed - but I will reiterate - she made sure that this is the case. She could have tried to spread the information everywhere, or better yet climbed to a position of power outside of Nobunaga's influence if her plan was just to mess around. Instead she's depicted as "not wanting to change anything", while doing almost everything to work against that.
Putting better weapons in tactics in their hands only makes the wars shorter and reduces the amount of suffering overall.
Untrue. Or do you need a reminder of the Vietnam war? Agent orange? Nukes over Japan?