Crit Cap
Maybe it's the 100% crit chance that makes it too strong.
Why not cap it....50% (maybe 75%, depends on the numbers) crit chance means you have to choose which crit items make the most sense.
It would also leave other builds viable when crit is strong...do I want more reliable damage per attack or potentially burstier crit chances?
Obviously that means reworking the strength of crit over all, but a crit chance cap could make it easier to balance.
on most champions and not in conjunction with any Energize items.
100% crit is 4 items and that means not getting 
or 
... or losing boots.
Even then no BT either.
Youre severely limited by trying for 100% crit and only Sivir or Ashe reasonably might do it.
If Xayah and Reaver work again then sure she'd love RFC+IE into reaver + Dancer or Reaver+Shiv+Razor