People bag her all the time saying she's bad. I don't think people realise how obnoxious she really is. Her only problem is that she can't lane, but she's like Jax in that she just needs 2 items to do damage.
I disagree with the bolded + underlined statement. Having played Irelia, her "free" secondary gap closer is big on initiating. Her double steroids allow her to go for advantageous trades, especially by level 3. She has the tools to excel in lane early on and is required to do so because she has no cc and doesn't build tanky. She is like at lower elo because she is one of the easiest champions to snowball and continue snowballing considering the enemy continues to be stupid or is a feast or famine champion like her i.e. Riven.
Even if you screw up and aren't able to capitalize on her power spike at level 3, you get another power spike at 6 which gives you immense burst to harass people under tower with no tower aggro as long as you just keep flash in your back pocket. When used in conjunction with ignite it is incredibly obnoxious. If you're still not able to snowball the lane by then they you will suffer in mid-game and in team fights which is frankly deserved.
Fiora is easily countered by people who actually want to shut her down. She's great in Solo Q because the Solo Q community is toxic and because of that people develop an insular direction of thinking that doesn't extend beyond their immediate concerns. Considering how few item actives there actually are in League of Legends, the fact that Zhonya's completely shuts down her ultimate means that an attentive mid laner can literally give her the middle finger if she's behind due to being countered in top lane and tries to burst you down to get a free kill. Considering how core Zhonya's is in the current meta it's easy to shut out Fiora during the first 20 minutes of the game.
Even if you dominate her, you still need to babysit her which many people in Solo Q hate. She can come back from being behind in lane if the top roams by getting free farm especially when she just builds Tiamat which gives her complete minion wave CS and allows her to push waves hard when combined with her steroids. Fiora is garbage in team fights when the enemy team is fighting as a team. Her only option is to go all in, she has an uncontrollable blink (the downside of Master Yi's Q), no cc to make escaping easier, and has paper thin defense given her items are likely all +AD. Her ult is uncontrollable and again stunted in team fights, you could possibly hit the tank or the Swain that popped their Zhonya's and then you got blown up without touching their back line. This isn't even covering the fact that many champions with stealth oriented abilities like Graves and Akali can completely stop her ultimate altogether.
Considering other meta picks like Tryndamere or Irelia, you have much more control over popping your ultl and getting your burst on to the ADC and also have more survivability to actually escape alive and come back into the same team fight. I believe that games this season were more protracted compared to games in prior seasons. Because it can make an incredible difference at that stage in the game when one person gets caught out and objectives are much easier to seize as an AD oriented champion that her intangibility becomes effective since people are unfocused and prone to play carelessly and get caught out which is where Fiora can easily assassinate the stray and capitalize that into a teamfight win or go for baron.
However, if Fiora gets shut down by a team that realizes the distinct advantage in shutting her down then the game should really be over by 20-30 minutes unless the team threw away their advantage by doing something stupid.