Miss Fortune is severely underestimated, I've personally never had a problem and until last night I was on a streak of getting fed and carrying every game I played with her for like 15 - 20 in a row. In Ranked, but mainly Normals due to me not playing Ranked really.
I've done well with her with and against Bronze, Silver, Gold, Platinum, and Diamond players while playing Miss Fortune, and actually some Platinum and Diamond players got really salty about it and just said "You got lucky MF sucks youre bad" while I was going 20-0. Clearly they were just salty, or I'm really lucky.
As for her Grevious Wounds? They weren't really that big of a deal and were extremely overestimated and it was so easy to simply ignore it since they only lasted 2 seconds. Miss Fortune was compensated with some buffs or issues to her kit were resolved. Her early - mid game is even stronger than it is now and I think It's awesome Riot is highlighting her dominant early - mid game power.
She has a lot other ADCs can't offer, to start off with, she is really flexible and can do everything an ADC can do but maybe not to the best extent. Her dueling isn't nearly as good as Vayne's, and her teamfighting isn't as good as Twitch or Sivir's, however she can both duel and teamfight very effectively. Her early - mid game is extremely powerful due to this, and while she falls off late game, she IS an ADC so she still does damage and can blow people up no matter what. She's a really versatile ADC that can do pretty much everything, there's always someone better at a certain category but never will they be able to be as versatile as Miss Fortune can be.
However imagine if her passive wasn't able to be shut off, her Q and E didn't have cast times, and her Ultimate could be casted while moving like Lucian's ult. She would be overpowered, you wouldn't be able to chase her, you wouldn't be able to run away from her, you wouldn't be able to win lane, and you wouldn't be able to win teamfights. Her damage isn't a joke, and she actually has a bit higher damage than most ADCs do. I don't think removing the cast time for E would be appropriate or even balanced, her slow isn't a joke either and It's severely underestimated, they actually just gave it huge buffs on the PBE too.