Is there ever really a point to opt for anything other than the highest calibre?
Higher calibres may demand additional weight and funds, but except in rare cases will always exceed smaller guns in every metric except hits-per-minute within short range. An all-big-guns BB with nothing but 18" guns will perform great against any ship type and at any range. Similarly, secondaries follow this bigger-the-bigger pattern. Other than cases of technology difference (Mk1 18" vs. mk5 14"), there's no reason to ever consider a lower calibre. Is this intended, or just part of the alpha process?