As mentioned above, I believe Werewolves were part of the curriculum, they just weren't upto them quite yet- Snape had just jumped ahead to undermine Lupin.
That's kind of what I mean about Lupin teaching about Dark Creatures- it was more about Snape being justified in jumping ahead a few lessons to Werewolves. It was more about Lupin than actual DADA. Yes- it's part of it and the Boggart lesson is always super popular with the fans (which is why they revisit the lesson in Fantastic Beasts- Crimes of Grindelwald) but yeah- I think facing off against Dark Wizards and learning about actual Dark Magic is a more valuable lesson.