Why Hood and Alaska are not the same ship type

Can Hood and the Alaska class be treated as the same classification of ship?

No: Hood was a battlecruiser with contemporary capital-ship armament, while Alaska was a large cruiser whose 12-inch guns sat below the U.S. battle line's 16-inch standard.

Gun categories change over time, so a calibre once used in battleships does not remain a capital-ship weapon forever. In the classification argued here, Alaska's 12-inch battery stood below the 14-, 15-, and 16-inch guns of contemporary battleships and belonged at the upper edge of cruiser armament. Increasing calibre offered more destructive effect when the rate of fire of an 8-inch gun could not be increased. Alaska is consequently treated as an enlarged heavy-cruiser development of the kind restricted by the Washington and London naval treaties, while Hood remains a battlecruiser.