> I mean, if you put guns instead of planes on a modern aircraft carrier you'd have a battleship that's a hell of a lot bigger than any battleships in WWII.

This is not true. The biggest battleship bought was the yamato

> Length: > 256 m (839 ft 11 in) (waterline) > 263 m (862 ft 10 in) (overall)

The biggest CV (aircraft carrier) right now should be the Nimitz class with

>Length: > 317m

which seems to emphasize your statement, but, battleships are not versatile and battleship development pretty much stopped after WWII. The germans had propsals of the H-class battleship, with a total length of the H-44 of 345m.