I guess that's sort of true, but you're leaving out the part where she's doing pretty terrible damage this way. Q tickles if it's not a second hit and only does substantial damage if it kills the first target. It's not super hard to do, but it's hardly reliable. Not like she just automatically chunks somebody's hp because she landed a 3rd AA.
The problem with her ulti is that it's not going to out-damage AAs. It's situationally useful (like for dragon snipes or jungle group fights or insta-clearing a wave under a tower), but it's not great damage in practice outside a wombo.
I'm not saying that she doesn't have a useful kit, but I am arguing that the pieces don't come together in a package that excels at actually securing kills and/or avoiding deaths the way many other adcs can.
Statistically, of the top ten ADCs right now, Miss Fortune has the 3rd steepest learning curve after Kalista and Draven. Morde, Jinx, Vayne, Ashe, Sivir, Varus, and Kog'Maw all have better results for players under 125 games.
Logically it makes sense that it's easier to point-and-shoot Q compared to a skillshot Q like Sivir or Varus. But what you're missing is that you only have to actually land one of those skill shots to have around the same impact as 3 point-and-shoot MF Qs. It's just a matter of time and odds that you'll out-damage MF, even with shitty aim, so it makes perfect sense.
Basically, I think you're right that she's easy to play. Poppy's also easy to play, but you can't expect good results unless you put more effort and skill into her than you would need to get similar results on a different champ.