There is no other ADC that has lower based AD as well. There is no other champion with lower AD growth who won't have higher base AD in few minutes as well.
You have to view champions holistically, not based upon ults. MF is a champion who is distinctly bad at single target DPS while being a marksman where that is one thing ADC is to excel at. There is a reason why players keep saying MF is nothing but an ult bot past laning phase. An ult where the majority of the damage can be walked out of or canceled while being stationary as the largest target in the game.
Now, the ult may be a little much right not because Riot overtuned Lethality so now people are actually playing her, but soon Riot will make adjustments and fix the both of those.
So yeah, it is pretty necessary.