The Alaska and Guam were indeed superior to the Graf Spee. As for being a battle cruiser, it is arguable if not clear. Your case of the main armament being less than contemporary battleship keels being laid is well taken, but there were still many old battleships then in service with main armament similar to the Alaska's. The desire by some to call them battle cruisers rests on their large (if not 15-16") guns and their fantastic speed. What this analysis leaves out is their excellent armor, which for a 16" gunned BB would have made it a battle cruiser, but for 12" guns made them well balanced.
It is my opinion that their 12 inch guns, comparable armor, and excellent speed made them fast battleships. Remember that it is not just the diameter of the gun, but its caliber. These 12" rifles were superior to most earlier 14" guns in range. Had they appeared in 1914 they would have been the best "heavy battleships" in the world. Coming on the scene toward the end of WWII, they were light fast battleships.
The 12" guns had a max range of about 21 miles, however th MK18 AP shell only weighed 1,100lbs or so. Your point on the effectiveness of the 12" vs older 14" is well taken.
Also from the same source the US Navy never considered the Alaska Class to be a battlecruiser but a large cruiser.
One other thought on the Graf Spee vs USS Alaska. IF the Germans had the Alaska off of Buenos Aires the British would have taken a real beating. But of course the Germans didn't so it is just idle speculation
Have a great day
Regards
alfa6 ;>}
Perhaps Alaska was "You think you know how to build a pocket battleship? Look at this Lady and weep." Stick them in the eye with a stick with a grin on your face and twelve inch guns at your back.