Yeah, that's true. Maybe not even a ring, but the biggest drawback of Meteor Swarm is that even a small amount of fire resistance negates a large amount of damage. Well, that and the typical "allows a save and SR", but that's the case for most blasting spells anyways. And I've heard it's good for blasting large amounts of mooks. I doubt Xykon's fought many enemies that were resistant to both Meteor Swarm and Energy Drain, besides Soon Kim.