Duke ran very different plays for Isaiah than they did for Cooper, Kon, or Sion. That, to me, speaks to the expected role. Was Jon maximizing what a role player did best, or was he avoiding what the role player couldn't do, or was it a bit from column A and a bit from column B? I'm not ready to assume anything at this point.
I disagree with Isaiah's first step. I thought it was fine. I couldn't agree more about the strength and, to a lesser degree, playmaker part. Getting to the rim may have been an issue for Isaiah, but once he got there, good things tended to happen. Isaiah finished at the rim better than Caleb, Tyrese, Cooper, Kon, and Sion. I'm not sure why you would assume that he won't be a strong rim finisher with added strength.
I may be misunderstanding your third paragraph. Isaiah took only 4.9% of his shots from midrange. That doesn't strike me as a high percentage. Why would that be a factor for Isaiah?