Lion and Vanguard follow different capital-ship lineages

Is the Lion class essentially a larger Vanguard hull fitted with 16-inch guns?

No; Lion develops the battleship line through King George V, while Vanguard draws more heavily on the fast battlecruiser lineage of Admiral and G3 concepts.

Lion pushes the Queen Elizabeth and King George V battleship tradition into a new 16-inch fast battleship. Vanguard instead reflects a different route toward a fully armored, high-speed capital ship, with stronger conceptual links to the Admiral and G3 battlecruiser families.