Stones isn't a great passer, what he's great at is bringing the ball out of defence, and getting past the first man. At some point people seem to have mistaken being good at bringing the ball out from the back, for being a fantastic passer, but they're completely different things, and Stones' passing is miles below the likes of Otamendi let alone Bonucci or Boateng.
What I will say though is that Otamendi's passing is miles better than it was 9 months ago, so Stones could definitely improve and get to the level of those guys. There's signs he's got the skill, he does occasionally hit a long bass that is brilliant or plays a great through ball, but it's pretty embryonic at the moment in my opinion.