"lets remove this and that from vayne's kit! that'll balance her"
or people could realize that Vayne's main problem is that her ultimate is on a very low CD and it's practically up everytime she gets into a fight or tries to assassinate a solo farmer.
A lot of ADCs get punished pretty heavily if they waste their ultimates on small skirmishes and don't have it up for a upcoming teamfight but Vayne doesn't really suffer this problem.
tl;dr increase her ultimates CD so she can't snowball as easily and has to rely on surviving the laning phase like she always has.

: 110/90/70
: 120/100/80
: 120/110/100
: 120/100/80
:100/85/70
:140/110/80
:120/110/100
:110/100/90
:2/1.5/1
:90/75/60
:90/75/60
: 80
:110/100/90
:2 - 12/10/8 recharge
: 90/75/60
: 100/90/80