I'd be more inclined to vote for Raseri or vyomov is their sets were Jolly. It's basically exactly what Raseri said in his post: "At +2 you outrun everything up to but not including Swellow..."
I feel like outspeeding Swellow is pretty important, though maybe that's just because I use Swellow a lot (more than I should), and I've run into a few Swift Swim Armaldo on the ladder that I've beaten strictly because my Swellow outsped their Armaldo in the rain.
Anyways, like I said, it's just my thinking on the matter. I love Swift Swim Armaldo and even got user: the wolf, to use it on her rain team. She's loving it because of how easily it can beat Grass-types, which rain teams usually struggle against. One thing's for sure: offensive Armaldo is undoubtedly better than Rapid Spin.