Whats the point of all the AP scaling in MF Kit?
I did some maths and full AD armor pen MF ult can do over 6000 damage with the following build.

On the otherhand, if MF had 900 AP(Which is hard to get nowadays), her ult will do a measly 3200 physical damage. Not only is the damage way less, but she has no access to armor pen.

So can anyone tell me the reason she has any AP scaling at all, because, it seems rather useless. Before I felt she had access to
slow, but with Rylies nerf, there is really no point in AP MF. It is not even close to how viable AD MF is.
So what the point of the AP scaling?