When heavy guns make sense on a fictional carrier

How practical is a 100,000-ton nuclear carrier with two twin 400 mm mountings in the Eighty-Six setting?

The heavy guns make sense for the setting's close-range threats, although the same arrangement is not favored for a present-day carrier.

Stella Matris in the Eighty-Six setting is presented as a 100,000-ton nuclear carrier with two twin 400 mm gun mountings. Its enemies create surface and airborne threats that can close far enough for heavy naval guns to matter. Under those fictional conditions, the armament has a purpose. The same arrangement is rejected as a preference for a carrier in the present real world.