i feel like fioras riposte is just wayyyy better than nocturne and sivir spellshield
imo i feel like its a powercreeped version of these abilities. Not saying fiora is op but if i was gonna nerf i would hit the riposte before anything else. Not only can it block numerous important spells/damaging abilities but it slows and can stun? Whoa. I know it has weaknesses because she cant move for the duration and its basically all her cc in one ability but wow, it feels so bad to engage on her and have all this bad stuff happen to you. Also, the fact that this ability is on a hypercarry makes it even more punishing. Shes a hypercarry that WANTS you to engage on her.
Again, not saying op, but i will say the ability is probably what makes her banworthy in competitive play.