I don't like that Morello isn't very slot efficient anymore. It's hard enough to get grievous on AP champions and I think it should at least be a better item if I have to delay my build that much.
One idea is to make Oblivion Orb higher AP and give it grievous but remove the magic pen: https://www.youtube.com/watch?v=XeiTZxXiWDo
However, even just bringing the AP back to 80 and raising the price by 100g would be reasonable. Considering the delay in buying the item, it's essentially power neutral.
BTW: As a total sidenote, it's really awkward to play vs Vlad as Corki. You can get Executioner but there's just no upgrade path. Morello is better on him than Executioner late game but it's still not great after his AP ratio nerfs.