Fenrir is a bit of a wild-card, in that he can either hit his target for paltry damage or completely knock them out and heal himself back up. He’s very strong when he kills his target as he will charge again very shortly afterwards too.
But I do think he’s a bit of a wild card. You have him in the best spot he could wish for though – right wing so he fires last and has the best chance to kill something.
I end up preferring him over Delilah mostly because of my preference. I think defenses with more bite are better. A center with Telluria + Delilah might be exploitable to allow the attacker more chances to set up skills – most of your damage is going to come from minion strikes + GM in the first 5~7 turns, until Jabber and Kestrel charge. I personally prefer offensive flanks behind a wall like Telluria who is already doing a “good enough” amount to keep her team alive.
That’s my reasoning anyways.