You could say the same about Vel Koz, or Nunu or any of the channeling ulti's. MF's ulti does massive damage and completely turns around fights, it's up to you to know how to position yourself and work with team. If enemies try to rush you while you ulti (after being cc'd especially) they take the full damage and can often die before they reach you (assuming you're not trying to 1 v 5) if they run away, they take a lot of damage and their engage is destroyed, so your team goes on the offensive while theirs is on the defensive, and with her passive, and ricochet it's hard to escape MF if you're losing the fight.
Graves Ulti is more of an instant mega damage, and doesn't need CC at all, but does need some good timing and accuracy. MF is much higher damage to MANY more target, if used during a minion clash too, you clear enemy minions while your proceed to add to the total damage (which only makes a difference early game or if you have baron or seige minions, but still)
Every champ is different and has times to use them. If you don't want to use MF, don't, if you don't like her how she is, use someone else, there's plenty of people that are fine with her and don't want her to get some SUPER Ulti buff, which would be followed by heavy nerfs in other areas