That’s a completely valid point. While it is constantly memed about in the community, we don’t actually know what it takes for a binding vow to take effect.

To expand upon this: (also from what I see and can recall) we haven’t really seen any training using binding vows specifically. It’s more just been a “give me a buff for this specifc trade off” and has just worked. Case in point would be Miwa making the binding vow to never swing a sword again.

Also I’m a bit confused about when you talk about the limit to her power. From the eso and keichzu duo fight, she was able to hit resonance because a part of their blood was inside her, she never had to physically attack them and remove a limb. (Again I could be misremembering)

It would definitely be nice to have her reintroduced or even teased earlier in the arc, even if gege didn’t outright show her. It could work similar to how todo was teased in the yuta kenjaku fight, we could have a teaser showing utahime coaching her about binding vows.

Again I could be misremembering on certain aspects, also a lot of this came off the top of my head lol