In competitive situations, a character like Fiora can get shut down. It's relegated to a last pick only situation, imo (kinda like how kat can work, how I think Malzahar can work, etc etc [realistically nearly everyone can come in as a last pick in the right situations]). A solid team comp requires at least two engage[ment forcing] champions, Leona/Thresh aren't always available, the best tops are solid but require assistance (renekton, shyvana, mundo), Fiora sits somewhere between a lot of damage and a "selfish play pattern"; she's a character who can go in and deal a lot of damage with relative ease, but it doesn't "add" to anything other characters can do, or will need to do, she's just damage. Jax requires focus, deals damage the longer he stays in fights (ramping up, Fiora kinda has this with her health regen + movement speed, but not really), negates focus (dodge) and has cc and a longer ranged blink.
If she can get shut down, and the only thing she offers is damage, means that if she isn't well farmed she's doing virtually nothing. If she's lost lane early, she's likely against a character she'll always lose against throughout the game (not always true), unlike Jax who has significant power spikes (tl;dr free-er stats than fiora) and is really only shut down indefinitely by MAYBE Malphite/Lee.
I agree she's broken right now, ever since they remade Yi (into what I think is a ****tier character), she's been an underappreciated super deeps and the continual nerfs to other AD casters when she has competitive burst, puts her into the forefront of "power level", but still has a restrictive kit.
Imagine if the lee change with 100% free attack speed actually was a thing, lol. Lol Fiora.