Eh..
I never considered Vayne to be anywhere Skill-related. You obviously become better as you practice with champions, but some (like Vayne) just don't seem to require all that much for you to dominate with.
Try to catch her? Well, she has her Q and E, so good luck with that. Try to run from her? Well, she has her Q and passive (Which gets a huge boost upon ulti activation)
These alone make her a -very- safe champion in my opinion, and on top of all, she gets an hard CC which applies her bread and butter ability, plus an AA reset that makes her deal more damage. Did I mention it has little to no CD or mana cost?
Two steroid abilities, hard CC, %HP ability, and easy to use engage\disengage tools, she is easily one of the safest ADCs out there.