The thing is that Miss Fortune, while she isn't the BEST duelist and nor is she the BEST teamfighter, she has a strong mix of both. She can outduel a lot, but not all ADCs, and she can have a much better teamfight than most, but not all ADCs.
She's like if you threw someone like Sivir and Vayne together but lessened their core strengths so she wouldn't just be the best ADC in every way...aside from infinite dashes which Riot definitely wouldn't allow to happen CoughKalistaCough.
Even if you're not fed, remember that people like Sivir, Lucian, or Twitch won't be doing much damage either unless they're at full build. This pretty much is the same with every ADC except Vayne or Kalista if played properly.
Miss Fortune is a pretty interesting ADC, she isn't the best at anything, but she can do it all at the same time. Due to this she has relatively no hard counters, and just last night where I got my fourth pentakill I was actually up against Quinn, arguably Miss Fortune's biggest counter. She synergizes in or against any team comp, and her early - mid game is insanely good. I would confidently say her early game is the best, especially now, of any ADC and I think her mid game is arguably one of the best of any ADCs too.
Sure, Vayne can outduel a Miss Fortune, and sure Sivir or Twitch can have better teamfighting. But Vayne's teamfighting? Unless you're Gosu with perfect mechanics, which I guess applies for mostly any champion, you're not going to be the best in teamfighting. Sivir in a duel? If you dodge her boomerang the only thing she has damage-wise is her auto attack resets, but even then Miss Fortune's auto attack resets do damage and have a much lower cooldown, Vayne's auto attack resets are on a 1 second cooldown and allow her to tumble.
I think a lot of ADCs have more defined strengths and weaknesses, but Miss Fortune's identity is being much more flexible. If you need an ADC that can teamfight really well, but also hold her ground more than well enough, she's a great pick and I'm quite surprised she isn't played more often considering she statistically does better than most ADCs. Now I'm not saying stuff like winrates are the BEST to go off of, but she's maintained around a 51.70% - 52% winrate throughout every patch since her last changes.