Which exactly is the type of war theatre this ship would have an advantage over an actual heavy frigate? The design is superb, btw.

Otherwise, it is true that a ship like modern frigate or destroyer have the same functions and possibilities. I wanted this battlecruiser to be able to operate independently of the major Task forces and even without an escort. It is equipped to fight submarines, surface ships and aircraft.

The problem here is that you hit right on target upon a question I put myself for quite some time... Are the shells fired by such a battleship yes or no capable to be destroyed by modern CIWS before reaching their targets? Let's suppose such a vessel of a nation at war with another one takes part on an action against a major port with important petrochemical instalations. This port's defense systems have obviously all types of counter measures to sustain incoming missles of any kind but... if together with a bunch of, say, some ten missiles fired at the same time by the attacking force, a battleship like yours shoots a broadside from some 30 to 40 km away? I have my doubts if the attacked nation's defenses are able to fight effectively all the ordnance coming in at the same time... especially if we have in mind the small size and formidable speed of all cannon shells shot by thye battleship's artillery.