GamePress
Giratina review on Gamepress
The review states that Shadow Claw/Dragon Claw is A and Dragon Breath/Dragon Claw is B. In practice, this is simply not true.
Both Shadow Claw and Dragon Claw should be A, since Giratina's only purpose is to sweep gyms out of weaker Pokemon, it has no purpose in raids whatsoever, where Shadow Claw would be used, and most Gym defenders are weak to Dragonbreath and/or resistant to Shadow Claw.