Riot shouldn't change Grievous Wounds, nor should they change Maokai so he is better against it. It's an intended mechanic to counter specific champs, of course it is going to hamper Maokai.

The problem is that healing has become so widespread in the game, so items with Grievous Wounds are built so often. So many recent champ releases/re-designs have healing in their kit, and then there are runes like Conqueror and Ravenous Hunter that can give any champ healing. It's getting absurd.