To answer your ranting, the system with which I choose the attack for the boss is based on how much damage it can cause with those attacks. I pick the move which would cause the highest damage (in this case, Giga Impact), and then I add to the slate all the attacks which would do at least 67% of Giga Impact's damage (75% in Hard mode). In the original slate I made, I included Earth Power because I forgot to factor in Solid Rock. However, after factoring it in, I realized it couldn't be part of the slate due to the excessively low damage output. Thus I rerolled with the new (shrunk) slate and got Hyper Beam and Giga Impact. I hope it's more clear now. If you ask Engineer Pikachu, he'll be able to confirm you this is the system working behind raids.