jrrrrrrr's Gyarados counter.
Jirachi, Metagross and Magnezone can challenge sets that lack Earthquake.
I would remove Magnezone off that list - unless it's running max HP, its chances of surviving a Rain-boosted +1 Waterfall from Gyarados is low. You could mention Magnezone alongside with other Flying-resists, such as Tyranitar, Rotom-W, and Zapdos, for being able to switch in on the turn Gyarados's charges for Bounce to annihilate it with their respective super-effective STAB on its way down; it's not always that Gyarados has a Sub up to protect it from such kills.
Otherwise, great prose.