Yeah Riolu is not an S-Rank or an A-rank Pokemon. blararara brings up many good points on how Riolu is used other than its standard Roar spamming role, but i think he exaggerates. I've been playing around with Riolu with quite some time and I haven't had many games where I swept a weakened team by Copy Catting my move or my opponent's moves. The truth is, Riolu is just too frail. In a tier where priority is only almost all teams, Riolu doesn't have many chances to shine. It's certainly a top-tier B-Rank Pokemon but I don't think it makes the cut for A-Rank.
kael: I WANT DESTROY HE
kael: HE DON'T RESPECT ME