Don't think a battleship is something like ultimate power, no single battleship has ever fought because they would be something near to useless.
In the single player of the vanilla story, each rheinland battleship for example has had an army of fighters, gunboats or cruiser which are supporting it. Making battleships able to pwn everything alone would result in more cap spaming.
There are 2 ways for creating a reasonable force:
1) get mass of one type of a ship (the large german submarine forces were easyly destroyed during the WWII once the allies found out how)
or
2) get many different types to be prepared against anything
Look at the equipment of a NPC Battleship (let's take the missouri)
it gots many different turrets, some huge main turrets for defence against capital ships,
some smaller defence turrets, some missile turrets and some flak turrets for anti-fighter purposes, don't forget about the dozens of fighters which could be unleashed, this combination out of all this different components is the strength of a battleship, and not having only slow firing turrets and a massive amount of armor....
