It makes little sense for her ult to scale off AP
Right now it is very confusing when looking at the rest of her kit.
Her ult:
- scales off AP
- channeled
- AOE skillshot
Even when you land a perfect ultimate, there is very little damage behind it (compared to other ADC ults) when you are building for her intended marksman role since it scales off of 20% or your AP. When you buy AP items, your Q and autos do mediocre damage.
It feels like her kit is working against you in that regard.
Examples of AP scaling ults that work well on ADC:


All of these champions have added benefits in their kits to combat the AP scaling ultimates.
- cc
- spam-able ult
- escapes
- AD & AP ult scalings
MF is immobile when in combat, has no hard CC, has mediocre range, and has a channeled ultimate that leaves her vulnerable while scaling off of AP.
Let's check out all the other ADCs dominating the meta right now

They all have an ability that allows them to escape, cc, or kite their opponents (even while in combat!).
It's simply not worth picking up MF currently with her glaring drawbacks when compared to other ADCs. She is a gamble.
Saving her mage build **as it is presented currently **is holding her back from being a respectable ADC in higher level play.