Are you saying Rubio is a long-term comp, or a comp for the next year or two?Ball has the most elite couple of tools in this year's draft, with his vision and passing ability. But his jumper (in terms of motion and while moving--he's solid spot-up), defense, and lack of any other offensive game are all issues.
Jason Kidd with a little less physicality is the commonly-stated upside, but Ball isn't in his world defensively (yet, at least). Kidd is so unique I really hesitate to use him as a comp for anyone.
I think Ricky Rubio with weaker on-ball defense and a little better spot-up jumper is realistic. And that's a useful player. And the upside beyond that is sort of Magic-lite...which obviously is a huge impact guy. There just aren't many guys with his kind of vision and passing skils.
Because the latter would be impressive. Look at last year's draft: the only top-10 pick who was within shouting distance of league average was Buddy Hield (after he was traded to Sacramento, at least), and he's 23 years old. Even highly-touted 20-21 year olds are seldom more than marginal NBA players who show flashes of potential.