This is one of those military machines, that if the Axis had many more of them, we might be speaking German and/or Japanese right now.
Japan had many war aims that can be fairly seen as irrational, but they were never so delusional as to think their island nation of 70 million could take over a huge country of 130 million on the other side of the world. While at the same time controlling China, which was the Imperial Japanese Army's overriding goal in life.
As to the vessels themselves, like all the big WW1-WW2 submarine cruiser ideas, they were dead-end experiments. Too slow to run, too big to dive quickly, too un-maneuverable to evade, too vulnerable to fight on the surface, they would be a destroyer skipper's dream target.
Well the links are to show a bit of frustration I have with those who think the battleship dead. The concept of arsenal ship may make the carrier obsolete in turn. Too often we have a fighter jock mentality--and my links just go to show that things can come back around...
The battleship was a weapon system optimized to fight fleet battles with other battleships a hundred years ago. That world is long gone.