It's not the equivalent of XL, we might not get XL games anymore since Capcom sued Koei claiming to have the patent for disc based expansions on consoles (specifically, softwares that unlock features by swapping discs with another game) - although they could just make them big DLC packs.
Anyway, SW4-II isn't really that. It adds one character, new story modes and the castle mode with different types of challenges. However, it removes all story modes from the base game, the Chronicles mode and the character creator (although you can still import custom characters from the original game).