Yeah, Z-Electric Terrain > Z-Hypnosis is definitely the way to go on this thing. Z-Hypnosis sounds good on paper but in practice it's way too luck based, and gets blocked by 2/4 terrains which is not great with how popular Tapu Koko and Fini are the atm. Also, if you're looking for a Hidden Power to hit Alolanwak with, HP Ground is the best option imo. It actually has some utility outside of beating Marowak, since it breaks through opposing Electric types, like Magnzeone.