Umm... Cait had mortal reminder and BotRK and Aatrox had BC and executioner's.
Grievous wounds doesn't stack, so that healing was with grievous wounds applied. If the target already has GW applied, then LDR does more damage to that target. Not sure why are you trying to act like that healing was without GW...
Yes, grievous wounds is counterplay to healing, but it's not enough. You go grievous wounds pretty much every game nowadays and there is still so much insane healing.
I did say you see it doing work in the 2nd half of the clip, when cait gets involved. I'm happy she's applying Grievous!