I can't help but think Mercurial Scimitar needs a nerf
Most problem AD champions currently work too well with it, as most of the counters to these champions is finally landing a hard CC on them (COUGH COUGH Kalista/Vayne/Fiora) Alongside is being a great defensive item (for ranged adc's) what allows you to not care as much about burst and is usually the item what allows them to just do as they please
and 
. Without that item, they would be top tier picks simply because that item didn't exist.
Yes CC from other teammates can break it, but when you can't rely on your team to break it, you have to do it yourself.