Why Is Fiora's damage basically unavoidable?

With two items + ferver of battle at level 18 she has 300 ad... each of her passive hits deal 15% of max hp in TRUE DAMAGE. That means she only needs to hit 1 vital, ulti, and in 5 hits she only has to deal 25% of your hp in anything other than true damage... Which if she has Iceborn gauntlets, good luck getting away from her, and with 300 ad those 5 hits are probably going to do more than 25% of your hp...

Also, if she times ripose correctly... good luck ccing her or dealing any damage while she 5 shots you with all her bonus movement speed...