To limit the Yamato Class Battlehips by reducign their defensive fire against air to a 4, then you also would need to increase them to THREE hits to sink.
Marianas Turkey Shoot. It was 200 and what hits to sink that single BB?
The Mushashi was sunk during the Sibuyan Sea phase of the Battle of Leyte Gulf, on October 24, 1944. It is estimated that the ship took 20 torpedo hits, 17 direct bomb hits, and 18 near-misses by bombs prior to sinking. After Action analysis by the US Navy and the post-war report done by the US Naval Technical Mission to Japan analyzing the loss of major Japanese warships (I have my own copy and also a complete set of the reports on microfilm) indicated that one of the reasons for the survival of the ship following so many hits was the relatively even distribution of them on both the port and starboard sides, in effect counterflooding the ship and preventing it from capsizing. Extremely heavy damage forward from both bombs and torpedoes resulted in the ship sinking by the head, and capsizing in the process of sinking.
The Yamato was sunk on April 7, 1945 during the attempt to sortie to the Okinawa invasion in an effort to attack the transport fleet. The ship was hit by an estimated 13 torpedoes, and at least 8 comfirmed bombs. I suspect that there were more unreported bomb hits, and no count was made of near misses. The US torpedo plane pilots had been briefed to concentrate their attacks on one side, and all but 2 torpedo hits were on the port side. The two on the starboard side were assessed at prolonging the process of sinking. The Yamato did capsize to port, and the after magazines exploded when she sank.
In neither case did the ships have fighter cover, so they were totally dependent on anti-aircraft fire from themselves and the rest of the task force. In neither case did the losses of US Navy aircraft attacking the ships exceed 10%. In comparable attacks on US battleships, Japanese attacking aircraft losses started at 50% and at times reached 90%. That is my basis for reducing the Yamato-class defensive fire against aircraft.
I am also very familiar with the protective schemes of both the Yamato and the Iowa class. The Yamato class did have a major flaw with its torpedo protection system that left it highly vulnerable to flooding from a shallow torpedo hit, to some extent compensated by the depth of the side protection system. There is also a problem with the torpedo protection system on the Iowa, which required modifying the liquid-loading scheme to restore full effectiveness. Overall, I would rate the Yamato and Iowa equal in damage resistance.
I guess that I am looking at it more from the standpoint of a naval tactical gamer where individual ship characteristics can be easily factored in, verses a strategic game, where that is hard to do so, unless you have a pronounced disparity. Also, keeping track of Three hits verses Two is much more difficult. I will have to come up with another way of factoring in poor Japanese AA fire. Two hits, and 5 attack and 5 defend it is.