I think I sent an ask like this to someone else too, but I feel that the writers thought of the idea of Yang sacrificing herself to save Ruby before ironing out the details surrounding it.
I feel like there are 4 major problems with that moment.
1: Neither Weiss or Ruby even tried to help Yang. I can kinda excuse Ruby, since she was in the middle of a fight, but when you give her a physics-breaking semblance, the writers kinda lost some excuses. Weiss doesn’t even try!
2: Yang running out of aura was dumb since we see Ren running out of aura for the… what?- Seventh time that in-universe day? Like… If Ren’s at full aura, then shouldn’t Yang also be at full?
3: We saw Maria tossing around Neo like a ragdoll earlier. You’re telling me that that elderly lady with cybernetic eyes can do that to Neo, but Yang can’t land a hit when Neo’s distracted in trying to kill Ruby?
4: Yang’s decision-making process was stupid here. Unlike Volume 3, where Blake was stabbed and vulnerable to splash damage, Ruby is holding her own against Cinder and is actively fighting, and therefore should have aura. So Yang could have tried to engage Neo instead of just taking the hit. Admittedly, this is Yang, so taking the hit isn’t out of character for her, but not engaging is also just as dumb! Is this what Tai’s whole “Your soul is a temper tantrum” thing led to? Yang deciding to just take a hit instead of fight? Which is what his ‘criticisms’ were all about correcting???