If damage cap wasn't a thing, she could be. A very, very specific use, but she could be!
But it doesn't seem like the devs care one bit about Sieg being useless.
EDIT: Game just got up, and I see this little thing:
-Battle support no longer available for raid event until you have opened the raid event page.
We got that like eight months in advance. Now we no longer need to see the "OMG WHERE MY REWARDS GO!?!?" on every single raid event. Yay!