Wulfen

Hello brothers of Fenris,
I have a question regarding the Wulfen. Why aren’t they used more often in competitiv lists? They have decent movement, are quite durable, have a 4+ invulnerable save, and hit really hard, especially against vehicles and monsters. Combined with a Rune Priest, they can take down a Knight if needed.
That’s why I decided to include 2x 10 Wulfen with hammers and storm shields in my list.
What’s your opinion on that?