Furai the problem with that is checking quaza. The only niche water arceus has really is checking common rain threats, and quaza at the same time, while being able to spread status. Mix quaza is almost impossible to check for sun teams without an arceus form, and though grass is superior in general it fails at this, and you also have no palkia check in the sun. If sr is down with your ho-oh grass arceus core, a smart palkia player will let you keep sun up and decimate you. Cm sets are very bad, because of the nature of the STAB, and you're vulnerability to status and ferro who you can't beat at all in your teams weather. Recover / ice beam / WoW or toxic if you run a fire blast as your last move.