I think if you're going to commit to running a weird set to have a mon 6-0 standard rain you should really commit to having a mon run a weird set to 6-0 standard rain. Guardian of Alola tapu koko is being 2HKoed by gyroball from ferrothorn while failing to 2hko back. Granted your opponent might set hazards assuming you switch out, but it still puts you in gren's shuriken range. Also if you fail to land Guardian of Alola on Ferrothorn you can do literally nothing to it while Focus blast from thundurus still 2HKoes.
Yeah Guardian + Thunder wouldn't kill it, as I initially assumed it would.
Thanks for the reply, and good points.