This is what I read: "he's taking a similar path as Steve McNair, who was a young player with the Houston Oilers. And I think that's a great analogy."
I don't see Carr and McNair "taking a similar path" in anything or see what McNair (or Pennington did for that matter) in their first two years as analagous to Carr's situation in any case other than they were/are all about the same age when they either started games or sat on the sideline watching. Carr has much more game experience at the same point in his career as either McNair or Pennington. I see Carr and Troy Aikman on the same path in their first two seasons in terms of production and experience and I can only hope that Carr stays on that path.
Pennington may have had no snaps by his third year but he was no rookie. He had 3 NFL training camps by then
Entering their third seasons Pennington had zero snaps as an NFL QB and Carr has what 1,500? That's even a more divergent path than McNair and Carr.