Executioner's Calling applies Grievous wounds with *any* form of physical damage for 3s.
Morellonomicon applies Grievous Wounds with *any* form of magical damage, including items, for 3s.
Mortal Reminder applies Grievous Wounds with *any* form of physical damage for a whopping 5s.
Bramble Vest and Thornmail applies Grievous Wounds for 3s when receiving an auto-attack.
Now we have Duskblade of Draktharr that will also apply Grievous Wounds for 5s, except this time it is conditional, requiring the proc of Nightstalker.
That's how it should be when applying Grievous Wounds. It shouldn't be so easy to apply with an auto attack or an aoe ability. You changed Quicksilver Sash so that it didn't negate the most important part of a champion's kit, yet you have Grievous Wounds incredibly easy to access and apply, hurting champions like Mundo, Soraka, Aatrox, Vladimir (even though he's really strong atm but that's not what this is about) and to a lesser extent, Darius, Singed, Warwick and Zac.
Yes, Grievous Wounds needs to exist to keep these champions in check. As someone with 1.5mil points on Soraka, I absolutely hate Grievous Wounds, but I don't disagree with it either and know it is necessary. But I also don't think Grievous Wound should be so effortless and easy to apply. Duskblade is the perfect example of how Grievous Wounds should be handled. Shutting down a champion so easily with just one item against them is a horrible feeling, especially when all they have to do is invest 800g into an Executioner's Calling to shut down a champion.
If you're going to make it so easy to apply, at least make it a stacking debuff, reducing healing by 10% per stack, up to 4 stacks with a 3s duration, each 3s reducing the stack by one instead of removing it altogether. This way it is much healthier to play with and against, without instantly reducing a champion to half of what they are.