Can't it be argued it's a design flaw? Shokaku-type was conceived between wars, and we know what that did for the Mk.14.
IJN carriers were prone to vapor fires, Taiho blew itself appart some time after taking a single torpedo hit.
"One of the Taihō's strike pilots, Sakio Komatsu had just taken off when he saw the torpedo wakes and deliberately dived his plane on the path of a torpedo in a vain attempt to save his ship. One of the torpedoes hit Adm. Ozawa's flagship, the 31,000-ton carrier, the newest and largest floating air base in the Japanese fleet in a part where her armor is thickest. The explosion jammed the ship's forward aircraft elevator, and filled its pit with gasoline, water, and aviation fuel. However, no fire erupted, and the flight deck was unharmed. Ozawa was unconcerned by the hit (
) and launched two more waves of aircraft. Meanwhile, a novice took over the damage control responsibilities. He believed that the best way to handle gasoline fumes was to open up the ship's ventilation system and let them disperse throughout the ship (
). This action turned the ship into a floating time bomb. At 1330, a tremendous explosion jolted Taihō and blew out the sides of the carrier."
I'm using NSM, so hitpoints don't play a (large) part in the damage model. Still, a hit to the engine room or below the bridge will doom a Shokaku class carrier.
If the model accurately models the way the ship was compartimentalized, I don't see the problem. I've been digging around for info on the hull designs, but I'm not turning up all that much, especially nothing to reinforce the theory.
You could get some material to consider here;
http://www.combinedfleet.com/shoksink.htm