I find it hard to believe he isnt physically mature enough for the NHL. Hes a big kid, and its not like hes super skinny. Sure he can add a couple pounds of muscle, but why do they NEED to do it during the season and not just save that for the off season where every other player focuses on weight gain and training then. If the ducks dont make the playoffs, hes going to have more than enough time to focus on that.
No one player is going to be great and consistent right from the start, they will all go through lulls and struggle at some point. Need to struggle to learn how to overcome it.
For Carlsson, by next season, I don't think it really matters if he played 75 games or just 60. I think the end result will be extremely similar, and would be nearly impossible to determine which route is more effective. But I do think withholding him from the lineup for this "strength building" in season will hurt the ducks team more as a whole (think thats easy to show through how the team is doing with or without him in the line up).