it's a thug life ¨̮
Swampert lives because Knock Off damage only applies once. CB cannot beat standard defensive Swamp in any scenario without a crit. CB Krook also desperately needs speed and cannot afford to go under 300 speed, otherwise it loses to Entei, Timid Blastoise at 280, and can't even revenge kill timid Togekiss.In my admittedly limited experience thus far, Terrakion's best set is subsalac SD. It's threatening enough that I am surprised only one mention of the set made it into the suspect paragraphs. Will be interesting to see how it fits within the overall meta.
In other news, everyone should try bulky CB Krook. It is deceptively bulky (survives Soul Dew Draco Meteor and Scarf Keldeo's secret sword etc) and hits monstrously hard, even against physical walls. To put it into perspective, Swampert risks a 2hko from Knock Off.
In general though, CB is relatively underwhelming; other mons like CB Scizor or CB Entei provide stronger wall-breaking potential while also adding some extra dimension, whether it's priority or a 50% chance burn, or a powerful U-turn. There are other mons that can be added to that list as well. Furthermore, since Krook can no longer check Latias and Mega Aero, it needs support to deal with those mons, which is extremely difficult since normally Krook is relied on to pressure those mons. Without Krook to effectivelly pressure those mons with a Choice Scarf or changing moves, it loses the ability to find as many chances to break walls and support its team to victory.