Same. I wonder if BB has a legit concern that Jones’ body wouldn’t last 17 games as a rookie.
I think that is a valid concern, Mac was a painfully thin freshman (180lbs) who managed to put on some weight by his senior year, but his body is still not at the development level of most veteran NFL QBs. No less than Brady said his body wasn't ready his rookie season. Different players physically mature at different rates. I'm sure Mac will be fine in a year or two.
But, as you say, I also wonder if he could last a full 17 games. Unless Cam gets injured (hopefully not) or absolutely stinks it up (and in fairness he has looked much better this year), I would rather see Mac on the bench until game 5 (Texans) or 6 (Cowboys).