Against Ho-Oh with solar beam, A-Golem's electric sub-typing removes the double weakness to grass, which *might* allow it to avoid getting one-shotted. It also loses the double weakness to water, which could also help it survive hydro pump from Lugia, if that ever makes another return. I'll admit, I haven't powered up/fought with any of my A-Golems, so I can't say for sure how well it would perform.
As for your Rayquaza team, forget Ice Castform and bust out the Delibird team with ice punch! š /s