Fiora is so disgusting.
Uncounterable damage output that scales of your hp and her ad is probably the most horribly designed thing out there. She will buy 1 life steal item paired with black cleaver because she can abuse the hell out of it and it makes her abilities always up at that point. Then she goes tanky and melts anyone she wants. Your tank items mean basically nothing at that point. Duelist doesn't mean she should be able to destroy the tankiest people in the game like their stats are nothing and you are just butter to her.
A duelist shouldn't have so much impact and pressure in teamfights.
She is allowed to build table duo to black leaver's armour reduction,her max go true damage,guaranteed crit plus ability to dodge spells.
then
for the CD. With the CD she has so much mobility, and can proc her passive on multiple targets easily.
and
she can crit for 600dmg from her E at max rank. Plus its like a 4s cooldown so its easy to one shot the carries while being tanky. she can also outduel any champ when being tanky because of her true damage and the CD being so low on her abilties