Armaldo is not really that great of a spinner mainly due to its typing and 4MSS, which brings forth some inconveniences. Its Rock/Bug typing means it cannot beat the Birds of NU such as Braviary and Swellow because it takes neutral damage from their Brave Birds. If it wants to Rapid Spin effectively it can't have Stealth Rock in its moveslot because it absolutely needs Swords Dance, Rock Blast, and Aqua Tail to break past the main NU Spinblockers in Misdreavus and Golurk.
Staryu isn't very good, but Recover does give it a niche in a way as its the only Rapid Spin user in NU with access to reliable recovery. Having Scald as a STAB helps because it hits Golurk Super Effectively and can burn Misdreavus. Even then its bulk is nothing to write home about and even some decently powered neutral attacks will 2HKO it.
Riolu is actually a pretty interesting Pokemon, but can be pretty hard to get it to work correctly or do anything other than Copycat Roar spamming. It would be nice to see someone finding the best possible set on the dog.