Were all-forward capital ships vulnerable to destroyers attacking from ahead?
Short answerNot inherently; their secondary guns could cover the forward quarters, the ship could manoeuvre, and friendly destroyers should screen it.
NotesThe six-inch secondary battery provides defence toward the forward quarters without relying on the heavy guns. Manoeuvre can bring those secondary guns into better positions as an attack develops. Friendly destroyers should also screen the capital ship. The forward concentration of its main armament therefore does not by itself establish a special weakness against a destroyer attack.