Apart from the unnecessary and frankly unpleasant mention of the 731 experiments you have a good point.
Should the Japanese decide to "break-out" from their pacifist history there is no doubt that within 5 years they could have most of the capabilities of some of the bigger players - an atomic bomb, long range rockets (but not maybe integrated in that time frame etc etc . Aircraft are a weakness as although they've expended zillions over the years they've never really manage d a decent aircraft programme. But if they turn their attention to electronic and cyber warfare they'd probably be leaders in less than 5 years.
But there'd have to be a complete U-turn in public opinion. I know very few Japanese who see anything good in militarism and the military