I love grim resolve in kill teams. It really makes it a gamble charging into DA. It also makes things like a heavy bolter nasty.
My go to list is 3 black knights and 9 scouts, with camo cloaks and heavy bolter.
This gives me 3 highly powerful bikers who can move incredibly fast and ignore the cover on kill team boards. It also gives me a surprising amount of bodies to pump out bolter shots with and get stuck in.
For survivability, you get 3x 3+ re-roll jink saves bikes. And 9x 4+ save marine bodies that can go to ground for a really good save.
For high str attacks, you have 3 mobile plasma-ish guns and a heavy bolter.
For low AP, you have the 3 mobile plasma-ish guns and can make one ignores cover. This usually equates to 1 model dead a turn at the very least.
And then you have enough bolter shots to deal with the remainder of the world.