Size matters, and steel is not the prime factor in military shipbuilding cost this day... 10-20 meters longer and the design is perfect
10-20 meter and the design is perfect, yes. but the world isn't perfect. For example here in Norway, the government controls everything the military build, so if you put forward a design like this one and an design that is 10-20 meter longer with just a little more capacity, the government will go for the small one, because that's how it works, they only look at the price tag, can they save a couple of millions, then they will save those millions.
and it is exactly the same in many other countrys.