You're likely in a higher level of play than I am, and you probably play MF far more than I do, therefore chances are your opinion are more right than mine is due to merits alone.
However, I have a differing opinion.
But her defining strength is AoE teamfighting.
It's not. And if it's supposed to be, I feel it could be a little more..."versatile". What I mean by this is that your defining her niche as "the AoE teamfight ADC" isn't all that great when the sole source of that niche comes from an incredibly difficult to pull off one-off R.
A powerful and devastating R if pulled off perfectly...but I disagree with it defining her in it's current state. Hell from my experience, often times it's better to not think too hard about it and just blow her load early so that I actually used her R rather than dying without using it.
Let's ignore the existence of 
whom I personally consider archaic and dated in design (just LOOK at her Passive!)
ADC's who have something that defines them often possess them when they need it, or have the capability express them often in a fight. 
's "magical artillery"-identity comes in the form of her basic ability W and spammy R. 
's "mixed damage assault"-assault comes from his entire kit and Passive. 
's "destroy everything in existence"-identity comes in the form of her Silverbolts. 
's "uncatchable prick"-identity comes from his free spammy dash...although I'd argue he's recently been dethroned by Runaan's Kalista.
Maybe if it's damage was heavily nerfed but compensated with a much lower cooldown to make it spammier. Then I can see MF as this "saturated damage across all enemies"-type ADC that'd really set her apart from other ADC's.
Again...I'm sorely aware that I have far less merits than someone who played her so much more successfully and often as me. However this is simply the sum of my experience playing all varieties of ADC. It's hard to see her as having any niche atm. What defines her for me atm is how she is the only one who lacks any of the 3 basic tools other ADC's have to stay alive. If you say her niche is AoE Teamfights, I can't argue with someone so much better at her than I am. But I will say that if this truly was the case, then it's not well pulled off due to that identity hanging solely off an overly conditional and one-off R. For me, what defines MF are her weaknesses, not her strengths.
Let me expand on the "AoE Teamfight"-identity a little more.
Do you know who I personally consider a better contender to fill that niche than Miss Fortune? 
.
Why? Because unlike MF, Jinx is capable of unleashing a CONSTANT and RELIABLE form of AoE damage in the form of her Q. In fact, thanks to her Q, Jinx's AoE basically became her basic form of attack! (60%-70% of the time) And this is all despite the fact that "AoE Teamfighter" isn't supposed to strictly be her niche. But she still feels closer to it than MF.
. Unlike MF, Draven's speed boost costs mana and isn't permanent. Sounds worst in theory right? Wrong, because he can choose to have it when he NEEDS it. Want to pursue? Press W. Oh shit, are you hurt and need to escape? Press W. Doesn't matter if your enemies are still shooting you, that MS boost is always going to be there for you.
