Sounds to me like your not looking hard enough. If Fiora has Sustain, Soft CC, a Block, and Health shred, Then she doesn't have hard CC or tankyness. Her kit is specialized for dueling. But she's still fairly vulnerable, and she can't handle a crowd.
[{quoted}](name=Raccoon Kid,realm=NA,application-id=3ErqAdtq,discussion-id=9ndnm0Ue,comment-id=00000000,timestamp=2015-11-06T03:54:12.456+0000)
This is a "Why is it okay for Fiora to do these things, but Cassiopeia doing these things would be too much" thread
Cass has the problem of Being an AP DPS. They are oppressive when they are able to reliably kill champions, And that's all they're good at. (With the possible exception of Azir who has turret siege.) The only way that becomes balanceable is if they are shifted to a late game trump card. (which is why they are balanced as Hypercarries.)
The bigger question is does it matter if champion X can only do 1 or 2 things, as long as they do them really well?