It's just so hard to find the sideboard slots in a deck like this in Modern. There are too many werewolves and not enough silver bullets. A personal problem I have with Collective Brutality on the side is that it's sort of a grindy value card (unless you're using it for Reanimator shenanigans on the discard) so it's harder for me to evaluate when exactly to side it in than a "shoot you in between the eyes" type card. Obviously CB comes in against burn because CB wrecks burn, but beyond that.... It's hard to cut the silver bullets. Maybe when Dredge goes away again and the Leyline of the Void can go away, that's eating up a huge chunk of sideboard on its own. I guess the Surgical Extraction isn't as necessary if I have such strong graveyard hate, but Surgical Extraction can also be good against combo decks if you Thoughtseize their key piece and then extract it out of the game.

I did end up adding Gonti, Lord of Luxury if for no other reason than that I want 4 4-drops to come in for the Bloodbraid Elf in the rare instances where Bloodbraid Elf is bad.

Now that I look at it, what are your thoughts on changing the Ancient Grudge to a 3rd Kolaghan's Command? They both hit artifacts, and the trade off would be "better against artifacts" for a better generalist card.