I think we are forgetting about Rotom...
I have not heard anyone mention rotom, and I think we are forgetting that it could be an excellent threat in the great league with thunder shock/ shadow ball/ thunderbolt. I really hope that they release it soon, maybe in time for the twilight cup? :)
Answers
I don't want to write anything off too soon but its stats don't really favor the CP capped Great League. Attack is weighted more in CP calculation and with Rotom's attack being higher than its other stats it could get taken down pretty fast. It also faces threats from Whiscash and Marshtomp being able to spam Mud Bomb, so a grass type is pretty much essential to carry alongside it. It makes a fast answer to Skarmory though, so it's got that going for it.
Also as mentioned earlier, it learns Ominous wind instead of Shadow Ball. it doesn't hit as hard but can help chew through shields faster. It could also be helpful against Deoxys-D, who's projected to be a Great League behemoth.
