Morgana's Passive should be changed

Currently, with a lack of proper spell vamp and with her current lack of power in any role except support, I want to suggest replacing Morgana's passive so that she once more has presence in mid lane, but without making her overbearing as a support.

Corruption Enemies hit by Morgana's abilities and auto attacks reduce their Magic Resist by 3/4/5/6, stacking up to 5 times. (Scales at levels 5/10/15)

While this seems like it might be overpowering, allow me to further explain it.

As a support, Morgana will not be building AP until mid game. This means that the power of her passive is reduced in the support role, particularly if her Marksman does not do any magic damage.

As a mid laner, it would once more give her presence as a safe farmer/stall champion without being overbearing like Heimer. Having her AP built sooner would also make this passive have its strength sooner.