A surviving pre-dreadnought still deters raiders

How useful could pre-dreadnought battleships have been in the Second World War?

They retained limited convoy and deterrent value because many surface raiders would still avoid their armour and heavy guns.

Greek use of older heavy ships in the Second World War suggests convoy escort as a plausible niche. Such a vessel would be slow and obsolete against modern capital ships or air power. It would still carry armour and heavy guns that a commerce raider might prefer not to challenge. Usefulness depends on the opponent and mission rather than on whether a ship can still fight at the front of the battle line.