Champions who are 'duelists' are given tools that make them able to fight any enemy 1v1, and they tend to get different types of kits designed to do that.
Jax gets tons of mixed damage and attack speed + counterstrike, ult tankiness, and stickiness with q.
Vayne get's 3 hit %max hp true damage, stealth, mobility, and a knockback conditional stun.
Xin gets armor shred, is impossible to escape from with his low cd gapclosing slow and knockup, can can force a 1v1 by knocking the enemy team away from his target
Zed get's multiple gapclosers for outplay potential, an ult that is effectively a damage amp, an auto attack execute passive, and way more escapes and farming tools then other duelists at the cost of not being able to stand toe to toe in an auto attack battle
Tryndamere has an untargeted gapcloser, an aoe slow + ad debuff, a heal, 35% crit from his passive, and can't be killed for 5 seconds during his ult which allows him to build glass cannon and still do his job
As for fiora, she doesn't do the raw physical damage of trynd, the crazy attack speed mixed damage of jax, the armor shred of xin, or the damage amp of zed. She doesn't scale well with attack speed or crit at all. Instead, like vayne, she has a conditional %max hp true damage passive which allows her to fight any type of enemy 1v1 if she plays her cards right.
Every duelist has something in their kit that prevents them from being itemized against to the point of being unable to duel with equal gold. Building full tank against trynd makes you survive for a few more autos, zed will still pop you with last whisper and ghostblade + ult amp pop, jax will keep autoing you like trynd, etc.
Fiora is a duelist, the "Grand Duelist", so like other duelists she has a kit designed to allow her to potentially fight anyone regardless of what items they build. She's not someone you can build tank and spam emotes at, you have to deal with her and you have to play her passive minigame the same as you have to try not to get auto'd over and over by trynd, jax, xin, vayne, etc. or try to minimize the damage you take during death mark to lower the pop damage.