You dont need any more breakdown. Hes not ready, period. If teams thought his skills were ready for coming in and starting right away he wouldve been picked much higher. There hasnt been that good of a pure passer in college in quite some time, the rest of his game is far, far behind.
I'm not sure how you define "ready". if teams didn't think he could play he wouldn't have been a lottery pick. Obviously, he's not Kyrie Irving or Derrick Rose, but Marshall will be okay. He's a natural PG that pushes the ball, finds the open man, and sets up his teammates. Marshall makes his teammates better simply by his ability to get them the ball in different ways. Marshall has a lot to contribute and can do these things from day 1.