That ult. Still requires her to stand still, and channel for 3 solid seconds now. Any non-brain dead is just gonna wait until she channels then immediately interrupt it, I mean, its not like there's not a plethora of ways to interrupt channeled spells. Instant silences, pop ups, stuns, or just using x/y/z gap closer and immediately killing her. I had a non-fed Annie burst me down in .56 seconds a few days ago. Guess what MF's ult our ranges Annie, but any player with half a bit of competence is going to save their flash EVERYTHING for MF when she starts to channel.
MF is the MOST positioning dependent ADC in the game, when you consider her Q bounce requires her to be in the right spot, and her Ult makes her a sitting duck, but this league of gap closers, requires you to literally be in a game of "Bots" to get a full ult off on any portion of the enemy team.
One strong channeled AoE, is not an excuse for her to have poor ADC Focusing ability with some of the worst AD scaling in the game.