She used black features on prototype cu chulainAyaka is featless.
Which do just about jackshit.She used black features on prototype cu chulain
Not only that, she used them on a cu that's explicitly weaker than regular CuWhich do just about jackshit.
Even if you want to be as generous as possible, you could argue that it could have possibly hurt Cu since he took the effort to swing them away instead of just letting his MR take care of it but since he bitchslapped them away so effortlessly , Shirou who reacted to a more adult and experienced version of him would at the very least be able to dodge them.
So in the end, it ammounts to nothing .