Here's the thing - by the time Iowa and Yamato were in use, the USN was building complete air superiority while the IJN was killing their own best pilots and planes. After the USN had a few years of beating up IJN ships, the IJN commanders were exhausted, low on trained men, aircraft and fuel. The Yamato couldn't even kill all of Taffy 3, and you think she'd stand up against an Iowa with air superiority and all her modern escorts.