Arceus-Fire is also reliant on the sun to reach His full potential, something which is quickly removed by the sea titan Kyogre who can swiftly drown Him with the use of Choice Scarf.
Specific sets to do with other Pokemon shouldn't go in the overview, IMO. You're trying to tell others what Arceus is doing, not what counters him. That sort of thing belongs in counters, not the overview. At the very most, you should say something like "The ubiquity of Kyogre and its Drizzle ability severely hampers Fire Arceus's ability to pull off sweeps, and this should always be taken into account when using it/Him."