The actual problem with both Fiora and Vayne isn't their % of max health true damage

Is their absurd mobility.

has a low cooldown dash that is also an auto-attack reset, and on top of that has a knockback (Condemn) that can stun you if you are near a wall. Also, as an ADC she can kite anyone. Vayne's ult is also a problem if you don't have a pink ward, red trinket, or ability that can reveal enemies. This isn't even to mention her passive, which makes it difficult to run away from her if you realize you can't kill her. active also means that it is difficult both to escape from and to stick to her.

's Lunge has an absurdly low cooldown that gets even lower when it hits an enemy. It has the same problem as Fizz's Playful/Trickster: It has a long cooldown early game, but its cooldown gets too short later in the game for what it can do. Combine Lunge with Fiora's passive and her E, and you realize that unless you have a long ranged dash (like Kha'Zix's evolved Leap) then you can't escape from her once she gets on you. It gets even worse since most Fioras buy either or .

Everyone complains about Fiora and Vayne's damage, when the actual problem with both of them are their insane mobility and self-peel in Vayne's case and sticking potential on Fiora's case. It is extremely difficult to kite Fiora or to escape from her, and it is extremely difficult to escape from Vayne or to get near her.