Seeing as Mutsu is absolutely a battleship and not a battlecruiser.
True, had you said Hiei, Kirishima, Kongou or Haruna, it would have been debatable (as those would never have worked in a line of battle. Hell, I imagine had they been where the British battlecruisers had been at Jutland, some of the Kongõ class would have exploded, I mean, they were all British designed battlecruisers). But Mutsu ... she's undeniably a Dreadnought battleship.