Let me clear this up.
DW3:XL has Musou(story) Mode for the 7 Others characters and more stuff(items, weapons, difficulty, etc.) But it does not have Musou Mode for the other 30+ characters. Also, I believe, you can't get all the weapons with just DW3:XL because some weapons need to be gotten on DW3 stages. (the stages on DW3 and XL are different) So that's why people say if you want everything you need both games.