The comparisons to Rio are just plain wrong, imo.
Rio at the age of 22, paired up with Lucas fecking Radebe I might add(!), was busy leading Leeds to the semi finals of the Champions League, and had been part of a quality England backline with Sol Campbell. John Stones on the other hand, was made to look a fool at various times over the past season and even in terms of his career as a whole, how much of a period of consistent form have we come across? The last 3 months of the 14/15 season maybe?
People say Rio used to have lapses in concentration, but tbf he was partnered with Mikael Silvestre during that period. Stones has had the benefit of being partnered with one of the better CBs in England, who could hold his hand and guide him through games. Yet, he still looked like a fish out of water at times.