I believe that of all the "never built battleships (Super Yamatos, Saint Andrews Class, Montanas, H Class, etc.) " the Montanas were the ones closer to being a reality. After some examination I came to this particular doubt:The US Navy tried to protect their ships against a ship with similar armament. They knew that wasn't the case with the Iowa class, and the Montana class would have been a much better balanced ship. It would also have had better TDS because the internal belt was not a part of it. The machinery arrangement was much better for limiting torpedo damage as well. IMO was a far superior design. The Midway class carriers used the same machinery arrangement.
Ironically, the secondary battery wouldn't have been as good for AA defense as the 5"/38s on the Iowas because the 5"/54 mounts designed for them were cramped and had some of the same problems as the British 5.25" guns. They were not popular with the gunnery depts of the Midway class carriers, which is where they ended up after the Montanas were cancelled.
Why, if there was the chance to design and build a brand new Battleship, the USN insists in a 16" gun instead of a heavier one: 18" or 20". The Montana had the potential capability to mount either. ( The US had the material capability to build it and rearreange the Montana´s design) That and considering that an earlier enemy BB like Yamato already mount 18"main guns. Moreover the British were considering the mounting of 18" on the Saint Andrews Class (but I doubt that in 1945 they were going to be able to build and install it). And the Germans had this idea of bigger guns in their early H Class (aprox 16") but, if opportunity arrives, to build the bigger ones with the 20" guns. So, if the US had the opportunity to build the Montanas then, likely, Japan, Britain and Germany (well, strike the Germans out of this!) would be able to put at sea units with heavier and more powerfull guns. In theory any of those projected BBs were superior, in terms of armament, to the Montanas. And it´s funny because the US was the major power with more options to build the bigger one.