Upvote:1
The Akagi was a battlecruiser, but when the decision was made for the second carrier, the Japanese wanted a carrier that was even larger than the Akagi, that is, more like a battleship than a cruiser. When the Japanese converted the Akagi, they "supersized" it, making it almost battleship size. The new "Akagi" was much closer in size to the Kaga than to the Takeo, so it would make much more sense to convert the Kaga into the Akagi's sister ship, than the Takeo. Also, the Takeo design was considered "topheavy."
The Japanese soon reconsidered their aircraft carrier designs, and two later ones, the Hiryu and Soryu, were smaller, lighter, faster ships. But by this time, the Takeo and Atago and been "downsized" to heavy cruisers.