Not necessarily true. Sure Arakune story-wise is a pain in the ass and plays no true part in the central story except eating Kaka babies and sounding like a raver high on ecstasy, but while literally NO ONE cares for him (give or take Relius), Litchi is the only one who is even fighting for him in the first place. And while the means to reverse him looks impossible, the fact he vaguely remembers her and gets hysterical when she appears shows that all hope isn't lost.
That being said, Litchi isn't betraying her friends for one disfigured guy--it's practically the other way around. Everyone is so busy fighting each other and doing their own thing they don't take time to listen to her cry for help. You might say Kokonoe, Rachel and Tager warns her what she's getting into, but she has no other choice. Especially when they practically refuse to help her.
Plus, it's a really nice sub-plot that does a good job of taking away from main story but doesn't make itself irrelevant.